No. 4463.

MARCH 13, 1909.

The Milroy LecturesON

DISINFECTION AND DISINFECTANTS.Delivered before the Royal College of Physicians of London on

March 2nd, 4th, and 9th, 1909,

BY R. TANNER HEWLETT, M.D. LOND.,F.R.C.P. LOND., D.P.H. R.C.P.S. LOND.,

PROFESSOR OF GENERAL PATHOLOGY AND BACTERIOLOGY, ANDDIRECTOR OF THE PUBLIC HEALTH DEPARTMENT,

KING’S COLLEGE, LONDON.

LECTURE I.

Delivered on March 2nd.

MR. PRESIDENT AND FELLOWS,—The subject I haveselected for the Milroy lectures which I have the honour todeliver to vou would, I think, have appealed to Dr. GavinMilroy, the esteemed founder of the lectureship. Amongother matters of importance in public health Milroy wasintensely interested in, and was the recognised authority on,quarantine, which has formed the subject of a course oflectures by one of my predecessors in this lectureship,Dr. W. Collingridge. Milroy, it may be remembered, was anopponent of the method of quarantine adopted in his day, bywhich all persons coming from districts invaded by epidemicdisease, or who had in any way come in contact with epidemicdisease, were rigorously isolated for a period and the shipwhich brought them might be kept in port for a considerabletime. Milroy may be said to have initiated the modifiedmethod of quarantine now adopted in this country, andwith that modified method disinfection of the belongingsof persons, of the ship, and the like, takes an importantplace. So long ago as the "forties" of the lastcentury Milroy had studied the question of disinfection,which was then beginning to be considered, and we findreferences to it in his writings. Thus, in 1847, dealing withthe question of cholera and quarantine, he says, 11 I mayremark that there is a tendency at the present time [1847],even amongst men who should know better, to attach anexaggerated importance to the use of what have been veryimproperly called disinfectant agents’-such as the solu-tions of chloride of lime, chloride of zinc, nitrate of lead,&c.-in guardi _ against the development and spread ofpestilential diseases. These substances have, indeed, the

power of correcting offensive smells, and of arresting moreor less completely the process of putrefaction ; and, as thewords infect’ and infection ’ have often been used even bymedical writers in a vague and inconstant sense, they arevery frequently associated, in common parlance, with thepresence of foul and putrid effluvia. An attempt was made,a few months ago, to make the public believe, that by meansof one of these so-called disinfectant’ agents, not only mightthe foulest odours be got rid of, and the deleterious gasesemitted from putrescent animal matters effectually neutra-lised--two very important points certainly upon manyoccasions-but even the development and spread of malignantfevers and other communicable diseases might be prevented.Now, this is a great and dangerous mis-statement, and onetherefore against which the unprofessional reader, more espe-cially, requires to be put upon his guard. There is no neces-

sary connexion between the existence of the most offensivestench and the presence of febrific miasmata ; and the onenuisance may be most satisfactorily extinguished, while theother remains little, or not at all, abated. Indeed, the verypossession of an efficient stench-destroying agent may notunfrequently lead, in certain circumstances, to the veryserious evil of getting rid of a temporary nuisance, while theremoval of the radical mischief is wilfully overlooked orneglected. The only genuine disinfectant’ is, after thismain point has been attended to, an abundant supply offresh water and of pure air." 1 He here very rightly objectsthat the employment of disinfectant agents will not put astop to an epidemic without the use of other measures, anddirects attention to a fact which is of still more importanceat the present time, when the "market," if I may so termit, is flooded with inefficient disinfectants without legal

1 Cholera and Quarantine, p. 40.

restraint-viz., that the use of a disinfectant engenders a senseof security which in the case of an inefficient one is unrealand may lead to disastrous results.Ten years or so later Milroy appears definitely to have

recognised the value of disinfection and to have admittedit as a part of the general measures with which to preventthe spread of epidemic disease. Thus, in his work on" Quarantine as It Is and as It Ought to Be," 2 published in1859, among other regulations which he formulated he says :" (1) Foul bed and body linen and other baggage of the sortshould not be landed when there has been sickness on board,or where any epidemic exists on shore, without previousthorough cleansing and disinfection" ; and (2) if disease hasbeen on board during the voyage or on arrival the shipshould be lime-washed and fumigated, as well as cleanedout and aired, before free entrance is granted."The subject of dis-infection obviously includes the con-

ception of infection, and a study of Milroy’s writings clearlyshows that he had definite ideas regarding infection, and,with the foremost thinkers of the time, was prepared toadmit that the contagious principle of contagious andinfectious diseases might be a living something. For

example, in 1847, discussing the nature of the infectionin epidemic cholera, Milroy refers to the widespread blightsand mildews in the vegetable world, and in particular to thepotato disease, which appeared in different quarters of theglobe. He says 3 "When we see such indubitable evidenceof the migratory course of the pestiferous something (let uscall it, with the forefathers of our profession, Tt Beeov, qtliddivinum, as a reverential expression of our ignorance), whichproduces a widespread and desolating epidemic in thevegetable kingdom, why should we hesitate in admitting theexistence of a similar, I do not say an identical, cause in thecase of epidemic diseases in the animal one ? It is well knownthat many sorts of blight among plants are unquestionablyowing to the existence of swarms of the minutest insecttribes which at particular times and in certain localitiesbecome developed and spread over a large portion of theglobe, sometimes irregularly and diffused, at other timesalong certain tracts which can be distinctly defined. Now,why may not some epidemic diseases, it has been veryreasonably argued, in the animal kingdom be owing to asimilar agency ? 1 There is certainly much to warrant theidea and, at all events, it explains, better than any otherhypothesis, many of the phenomena of the moving course ofsuch maladies as the cholera and the influenza."

Milroy also had very clear conceptions of the variableinfectivity of different infective diseases. Writing on thesubject of quarantine in plague in 1846, he says : " Thereare certain maladies which can only be transmitted or com-municated, when either the diseased part in the sick person,or matter taken from it, is brought into immediate contactwith the body of a person in health. To this order belongthe ringworm of the scalp, the itch, syphilis and gonorrhoea,cow-pox (in man at least), hydrophobia or rabies, &c. Thesemaladies are incapable of contaminating the atmosphere,and persons, for ought we to know to the contrary, mightremain for days and weeks in the company of patientsaffected with any one of them without the risk of catchingthe disease, provided all contact, direct or indirect, becautiously avoided. It is to this order of diseases that theterm contcgaozcs should be strictly limited. The second orderof transmissible or communicable diseases contains thosewhich are propagated by the atmosphere, around a patient,becoming infected or contaminated by a peculiar effluvia ormiasm which emanates from his body, and which, beinginhaled into the lungs-and admitted, it may be, at the sametime into the stomach-of a person in health, has the

property of inducing like symptoms in him. Whooping-cough and scarlatina are examples of this order of com-municable or transmissible diseases. They propagate them-selves by infecting the atmosphere, hence they are properlycalled infectious." He adds that there are certain diseaseswhich are communicable both by contact and through theatmosphere, e.g., small-pox and glanders, and suggeststhat such might be termed contagio-infectious. It will thusbe seen that, as regards the nature of the contagious or the

2 Milroy : Quarantine as It Is and as It Ought to Be (Savill andEdwards, London, 1859).

3 Milroy : The Cholera Not to be Arrested by Quarantine (JohnChurchill, London, 1847).4 Milroy : Quarantine and the Plague (Samuel Highley, London, 1846).

L

742

infectious principle, Milroy quite accepted the idea that this C

might be a minute living agent, and discussing the origin of a

human epidemic diseases he likens it to the potato disease, o:

and says: I I We need scarcely say that we are quite gignorant of the cause of this as of most other like visitations. c,

Is it of insectile origin 2 Many circumstances seem to grender this idea not improbable." r

Accepting the validity of the germ theory of infective r1

diseases, of which I presume it will be admitted there can be a

no doubt, the nature of the contagious or infectious prin- o

ciple becomes clear ; it is the living organism causing the t:disease. By disinfection the power which the living organism i]

possesses of infecting a healthy individual or animal is a

destroyed; and this may be brought about by natural t

processes or by the adoption of artificial means whichinclude the use of disinfecting agents, e.g., heat, or of dis- t

infecting substances, the disinfectants, certain chemical v

agents which act upon the infecting micro-organisms and s

diminish or destroy their vitality. The term " disinfection " r

may be employed in two senses, for while the destruction of 2

the power of infecting usually entails the killing of the finfective organism, it does not necessarily do so. For Iinstance, the prolonged action of relatively low tempera- ttures or of weak disinfectant substances may bring about asuch an attenuation of the microbe, such a loss of virulence, tas we term it, that it no longer possesses the power of t

infecting. Such an action must, however, be an unsatis- i

factory one to aim at artificially, and nothing short of 1complete extermination will satisfy the present day (

hygienist. <

Thirty-six years ago a distinguished Fellow of this College, (

Dr. Edmund A. Parkes, defined disinfectants as "sub- 1stances which can prevent infectious diseases from spreading ]by destroying their specific poisons." In 1875 another dis- i

tinguished Fellow of the College, Dr. Buchanan Baxter, insome valuable work on this subject, adopted the followingdefinition of disinfectant : ’’ Any agent capable of so modify-ing the contagium of a communicable disease, during itstransit from the sick to the healthy individual, as to depriveit of its specific power of infecting the latter." Baxtertherefore used the term ’’ disinfection" in the sense ofdestruction of the power of infecting, while Parkes employedit as denoting the destruction of the specific poison. Ithink it preferable to employ the former definition (destruc-tion of the power of infecting) only in connexion withnatural processes, while artificial disinfection should alwaysimply, and should be restricted to, the destruction of thevitality of the infective agents, the micro-organisms or

parasites-that is to say, in the words of Parkes, thedestruction of the specific poison.

It may be of interest briefly to survey some of the naturalprocesses which bring about disinfection, as they have somebearing on the artificial methods employed in combatinginfective diseases. Nature’s methods of disinfection-thatis, the removal of infective power-only partially depend onthe killing of the infecting organisms. Outside the bodyvarious agencies are always at work which tend to lessen thepower of infecting possessed by micro-organisms to such anextent that ultimately infection may become impossible.Probably in all cases a certain dose of the organisms isnecessary for infection to occur, and thus dilution of theinfective material with a relatively large volume of air, orin some instances of water, may so reduce the dose ofinfective matter which can be admitted into the body at anyparticular time that infection does not take place. Therecan be little doubt that the dilution of infective matter byadmixture with the air plays a considerable part in prevent-ing the spread of epidemic disease, and therefore in ourfever hospitals liberal air space is regarded as essential.In the air, too, the bactericidal action of sunlight is likely toexert a maximum effect. Desiccation, though to some extenttending to promote the spread of infection by favouring theformation of dust and so serving to disseminate the infectingagent, largely acts as a disinfecting agent by the act of desicca-tion destroying the vitality of the infecting organisms. Aninstance of this is met with in the case of the bacillus coli.The streets of all our large towns must be literally swarmingwith this organism derived from the excreta of domesticanimals, yet it is exceptional to find bacillus coli in the airof cities. Thus Gordon 5 examined the air in the East

5 Report of the Medical Officer of the Local Government Board fo902-03, p. 421.

entral district of London, exposing dishes of broth for onend a half hours to the air ; bacillus coli was obtained onlynce out of five experiments. In 500 litres (or about 125allons) of air aspirated through salt solution no bacillusoli was found. At Blackheath 1000 litres of air (250allons) were similarly examined; again with a negativesult as regards the presence of bacillus coli. Similaresults were obtained by Andrewes 6 exposing plates to their in the vicinity of St. Bartholomew’s Hospital; no coloniesf bacillus coli were obtained, and this investigator remarkshat Bacilltl8 coli and its allies are of very sparse distribution0. the air of the City of London I It appears, then, that the,ct of desiccation necessary for Bacilltts coli to gain accesso the air is generally fatal to the organism.Filtration is another of Nature’s methods of disinfection

IY exclusion. Its action is best seen in the case of watervhich, percolating through the soil or through pervioustrata, such as chalk, becomes purified by the mechanicalemoval of the micro-organisms it contains. We artificiallyLpply this mode of the prevention of infection in the sandiltration of water and in the use of porcelain filters for themrincation of water. In man, filtration of the air throughhe channels of the respiratory tract almost certainly acts asL protective mechanism. Thus, in ordinary circumstancesjhe respiratory mucous membrane below the larynx is prac-tically sterile. The fact that inspired micro-organisms dolot as a rule reach the air cells of the lungs was first

jointed out by Lord Lister, who based his statement on the)bservation that in simple fracture of the ribs with wound)f the lung and pneumothorax infective pleurisy does not)ccur. This observation was explained by the fact that theitmosphere inhaled is filtered free of germs by the airpassages, "one of whose functions," he says, is to arrestinhaled particles of dust and prevent them from entering thelir cells." 7 StClair Thomson and I likewise showed 5

Ghat while it may be a common event in London for 14,000or more organisms to pass into the nasal cavities every hourduring ordinary tranquil respiration the mucous membraneof the deeper cavities of the nose is comparatively sterile,the organisms being arrested by deposition on the moistmucous membrane near the entrance and being expelled bythe trickling of the nasal secretion and by the action of theciliated epithelium.

Light, particularly sunlight, is definitely germicidal andacts both by a direct action, due to the chemical rays at theviolet end of the spectrum, and secondarily, by inducingchemical changes in the substratum whereby germicidal sub-stances, such as ozone and peroxide of hydrogen, are

generated. It can hardly be doubted that in the air, at anyrate, the disinfecting action of sunlight plays a considerablerole in the destruction of infective matter. Experiments wererecently carried out in India under the direction of Lieu-tenant-Colonel D. Semple and Captain A. W. Greig 9 on theeffect of the Indian sun on the vitality of the typhoidbacillus. The method employed was to soak squares of whitedrill cloth (1 square centimetre) in urine containing typhoidbacilli. The pieces were then exposed to the sun, other

pieces being kept in the dark for controls. At intervals apiece was taken, thoroughly washed in 1 cubic centimetresterile physiological salt solution, and the number of bacilliestimated in the washings by plating. The result was that;starting with an initial number of 240,000, after 30minutes the number was reduced to 1000, after one hour tofive, and after two hours and upwards none remained alive.The sun temperature was 1050 F. and the shade temperature920 F. In another experiment the typhoid bacillus was killedafter an exposure to the sun of one hour. Of the controls,kept in the dark, starting with an initial number of 240,000.after six days 25,000 typhoid bacilli were still alive, andthey had died out only after ten days.Our countrymen, Downes and Blunt, in 1887 were the first

to demonstrate the germicidal effect of light, and they showedthat the blue and violet rays of the spectrum entirely preventthe growth of bacteria, while the red and orange rays merelydelay development. The late Professor Marshall Wardshowed that sunlight killed anthrax spores by the directaction of the chemical, the blue and violet, rays, and not

6 Ibid., 1906-07, p. 197.7 Brit. Med. Jour., July 18th, 1868.

8 Transactions of the Royal Medical and Chirurgical Society,vol. lxxvii., 1895, and THE LANCET, Jan. 11th, 1896, p. 86.

9 Scientific Memoirs of the Government of India, No. 32, 1908.

743

through changes in the medium. Unfortunately, the activerays are very readily absorbed and have little power of

penetration, so that in an opaque substratum superficialdisinfection alone is obtained. In clear water, however, thegermicidal action of sunlight may be exerted to a depth ofsix feet.

I have recently, in conjunction with Mr. J. E. Barnard,carried out some experiments on the germicidal action of theviolet and ultra-violet rays which are so abundant in the

light derived from the mercury vapour lamp. These experi-ments (which are being continued and will be published indue course) show that a considerable germicidal effeet ismanifested on an organism like the Bacillus prodigiosus evenat some distance from the source of light and suggest thatthe mercury lamp might in certain circumstances beemployed for practical disinfection.The variations in virulence of pathogenic micro-organisms

which are well known to occur must to some extent determinethe occurrence or no of infection as well as of the severity ofinfection. Desiccation, light, and heat of a certain degreeof intensity all diminish virulence, and finally the decline ofan epidemic disease may coincide with a natural diminutionin the virulence of the infecting organism. For instance,during epidemics of plague, in the seasonal intermissionswhich occur the plague bacillus may be met with in anattenuated form, and the same may be the case at thebeginning-e.g., as pestis minor-and at the end of the

epidemic. Symbiosis, the growing together of various

species of micro-organisms, it can hardly be doubted, playsa large part in nature in the destruction of infectiveorganisms. Just as a vigorous weed, if allowed free growth,will overgrow and crowd out a less vigorous species, so theless vigorous disease-producing organisms may be destroyedby the vigorous saprophytes outside the body. The action

" symbiosis in thus "crowding out," to use a common

xpression, pathogenic organisms probably largely dependson the products produced by the symbiotic organisms havinga germicidal effect on the pathogenic organisms. Urine, forinstance, soon undergoes an ammoniacal fermentation withthe production of much alkali, and Colonel J. R. Forrest,R.A.M.C., and I have shown that even weak alkalies have amarked bactericidal action on some organisms.10 For

example, a weak solution of ammonia, containing 0’5 cubiccentimetre of strong liquid ammonia in 600 cubic centi-metres of physiological salt solution, had a completegermicidal effect on the typhoid and cholera organisms, apartial germicidal effect on bacillus coli and micrococcuspyogenes aureus within the time of xeperiment as shown bythe following table :-TABLE L-Germieidal Action of a Weak Solution of Ammonia

(0-5 Ct6bic Centimetre of 8trong Ammonia in 600 CecbicCentimetres of Physiological Salt Solution).

(a)

The action is striking in the case of typhoid fever andparticularly so in the case of cholera. With cholera thegermicidal effect was so rapid that within a few seconds, thetime elapsing between making the mixture and plating, a

10 Journal of the Royal Army Medical Corps, February, 1904.

large proportion of the organisms was destroyed. Fascesalso undergo fermentation with the production of acids or ofalkalies which are detrimental to pathogenic intestinal

organisms, such as the typhoid bacillus. In the Indian

experiments already mentioned, it was found that the

typhoid bacillus in fseces and in sewage dies out in from10 to 17 days. The acidity of the gastric juice in man

probably serves as a protection against typhoid fever andcholera, for the late Allan Macfadyen 11 found that in a

fasting animal given cholera vibrios in a little water, thevibrios passed on into the intestine, whereas when digestionwas in progress-i.e., when the stomach contained the acidgastric juice-the cholera vibrios were not found in theintestine. The fact that the lower animals do not becomeinfected through the digestive tract with the typhoidand cholera organisms (although the organisms may bepathogenic to the animal by inoculation) Metcbnikoffhas ascribed to the intestinal flora-i.e., symbiosis.Again, in some instances the conditions obtaining in the

living animal seem unsuited to the growth and multiplicationof certain micro-organisms, or the protoplasm may have noaffinity for their toxins, so that intoxication or poisoningdoes not ensue. Lastly, there are the active defensivemechanisms of the body which prevent infection ; thewonderful phenomenon of phagocytosis by which variouswandering and fixed cells of the body ingest and destroy theinvading bacteria; the formation of antibodies whichneutralise the toxins or bring about the digestion and solu-tion of the microbes ; and the development of bactericidalsubstances from the body cells and fluids which act as germi-cidal agents. From this survey it is evident that artificialdisinfection as a rule has little or no analogy with thenatural processes which prevent infection of the livinganimal.

I do not intend in this course of lectures to enter into themethods employed in practical disinfection; these, theiradvantages and disadvantages, are fully discussed in everyhandbook of hygiene. I propose, after touching on certainaspects of practical disinfection, to deal with the principlesunderlying the process of disinfections and the methods ofdetermining germicidal power, and finally to survey brieflysome of the regulations as to the sale of disinfectants.With regard to disinfectant agents, heat in some formis by far the most important and most generally used,others being of subsidiary value. Heat may be employedin the form of fire or in the form of high tempera-ture, either as dry or as moist heat. Fire is, ofcourse, the. most efficient, and there is one form of itwhich I should like to see in more general use than seems tobe the case. I refer to a torch flame generated by a cycloneburner burning paraffin gas oil driven by a pump through ahose attached to an iron pipe-an apparatus in some respectssimilar to the " fiares " used for illumination on night worksor in the thoroughfares in foggy weather. It has been veryfavourably reported on by Stiles 12 and might be employedfor the disinfection of surfaces, brick, earth, iron, &c., whichwould not be damaged thereby, such as stables, pens, yards,mud floors of native houses, and the like. Those who use itsoon become sufficiently expert to treat even wooden surfaceswithout burning them. Dry heat has been largely given upin favour of moist heat except in special cases-e.g., inbacteriological work for the sterilisation of vessels, &c.,because it has little power of penetration and becauseunless carefully regulated it is apt to scorch, as the tem-perature required for efficient disinfection is only a littlebelow that which scorches. For it has been found that micro-organisms in the dry state require a relatively high tempera-ture to insure their destruction-a temperature considerablyhigher than is the case with moist heat. With regard tomoist heat, even the boiling temperature is fatal sooner orlater to all micro-organisms, and a moist heat some 200 or300 F. above this is still more efficient, hence the general useof steam under pressure in apparatus for disinfection.

Although I have little practical acquaintance with steamdisinfecting apparatus, from theoretical considerations I haveno doubt that apparatus in which the steam is saturated (andnot superheated) at the particular temperature employed are.to be preferred.

11 See The Cell as the Unit of Life, J. and A. Churchill, 1908,p. xii. ; and Journal of Anatomy and Physiology, vol. xxi.

12 Bulletin, No. 35, 1902, Bureau of Animal Industry, U.S.A. Depart-ment of Agriculture.

L 2

744

The use of disinfectant substances or disinfectants,chemical agents which exert a germicidal or killing action ton micro-organisms, may next be considered. Incidentally e

it may be noted that in the case of infective diseases no pchemical germicide has yet been discovered that can be iintroduced into the body in sufficient amount without ’]deleterious result on the body to exert a general germicidal ieffect on the infecting organisms, except in the case of 1:

protozoan infections. In malaria, quinine ; in syphilis (now &Igrave;

generally regarded as protozoan), mercury; and in some iforms of trypanosomiasis, aniline dyes, atoxyl, antimony t

salts, and similar substances are efficient, but no bacterial sinfection has yet been found to respond to any chemical 2

germicide. Bacteria, which are vegetable cells, seem to be (

much less susceptible to the action of poisonous substances tthan animal cells, including protozoa. It is exceptional to 1meet with a substance which is germicidal on bacteria I iin a dilution of 1 in 5000, and such substances-for ex- I

ample, the salts of mercury and silver-are very poisonous sto animal cells. On the other hand, quinine has an appre- <ciable action on amoebse&mdash;for example, in a strength of 1 in 1

50,000, and although the question is still in dispute the cgeneral opinion is that quinine acts beneficially in malariaby directly killing the malaria parasite.13 The salicylates 1are practically specifics in acute rheumatism, and since there <

is nothing in their pharmacological action to account fortheir beneficial effect Dixon 14 suggests that this disease may i

be caused by a protozoon and not by a bacterium, and thatsalicylates may exert a specific effect on this protozoon just Ias quinine does on the malaria parasite. I

It is always hazardous to prophesy, but it appears to methat if any substance is to be hoped for that will exert ageneral germicidal effect in bacterial infections it will beobtained either by raising in some way the bactericidalaction of the body fluids of the infected animal, or by I

bactericidal substances derived from the tissues, cells, or

fluids of other animals or plants, or indirectly by the treat-ment of animals so that bactericidal serums are formed in amanner analogous to the preparation of anti-serums.The use of disinfectants, therefore, resolves itself into the

employment of germicidal substances : (1) in the treatmentof wounds and local infections, though even in these theymust be employed with caution and discretion; (2) for thesterilisation of instruments and materials used in surgicaland medical practice ; (3) for the prevention of the bacterialinfection of drugs-e.g., anti-serums and solutions for

hypodermic administration-and for the preservation offoods and other substances ; as regards these last the actionaimed at is usually merely an antiseptic one, the _preventionof bacterial development rather than true disinfection ; and(4) for the destruction outside the body of infective matteremanating from infected animals and plants.

I shall limit my remarks to the consideration of thedestruction by disinfectants of infective matter outside thebody, by far the most important use to which disinfectantsare applied, as in the disinfection of utensils, soiled cloth-ing, the dejecta, closets, &c., and the walls and floors andarticles of furniture in habitations where cases of infectivedisease have occurred. With respect to the habitationitself, it is customary to disinfect the rooms by fumigation,spraying, and general cleansing. Fumigation as ordinarilypractised with sulphurous acid gas generated by burningsulphur and other means I cannot help thinking is of

questionable utility as regards actual disinfection, though ithas some value owing to the thorough aeration which isafterwards ensured. The Clayton gas, obtained by burningsulphur at a high temperature, seems to me from some

experiments I have done with it to be far more efficient thanordinary sulphurous acid and has been favourably reportedon by Wade and Eyre 15 for the Local Government Board.This process has been extensively utilised for ship dis-infection, but has not been employed to any extent for housedisinfection though presenting several advantages for thispurpose, and it appears to me to be worthy of extendedtrial. Formaldehyde, when properly applied, is probablymore active than sulphurous acid, and chlorine gas still moreso, but is difficult efficiently to employ in practice.

13 Laveran: Trait&eacute; du Paludisme, ed. ii., 1907, p. 474.14 Practitioner, February, 1909, p. 245.

15 Report to the Local Government Board, No. 232, 1906, and Haldaneand Wade, Report of the Medical Officer of the Local GovernmentBoard, 1903-04, p. 330.

Owing to the inefficiency, as I believe it to be, of fumiga-tion as ordinarily practised, spraying and washing withefficient germicidal solutions must, I think, be regarded aspreferable. Some hygienists are of opinion that the dis-infection of the habitation is of secondary importance.They urge that the infective matter is attached to theindividual and his immediate belongings-clothing andbedding-rather than to the walls, ceilings, and floors of thehabitation, and from recent work we know the paramountimportance of the bacilli carriers in spreading infection intyphoid fever and diphtheria. On these grounds, therefore,some would limit the treatment of the habitation to thoroughaeration and general cleansing, reserving disinfection for theclothing, bedding, utensils, &c., only. Thus Firth 16 reportsthat, pursuing this policy in the case of scarlet fever, he hashad no more secondary and "return" cases than when themore elaborate methods of disinfection of the habitationhave been applied. If a fact, it would certainly muchsimplify the procedure in cases of infective disease; but onlyan extended trial, and one which most medical officers ofhealth would probably be somewhat chary of venturing on,can give us the necessary data.

School disinfection, again, is another matter now comingto the fore. Some sanitary authorities-e.g., those for thecounties of Buckingham and Notts and the East Riding,Yorkshire-are applying systematic disinfection by sprayingand washing with disinfectant solutions in the schools witha view to ascertaining whether the incidence of infectivediseases among the pupils is reduced thereby. The EducationCommittee for Buckinghamshire has been experimenting onthe disinfection of schools under its control for some monthspast, and I had hoped to be able to give you the results sofar obtained, Unfortunately, owing to various delays, thereport will not be forthcoming until the middle of this month(March). In a preliminary report published at the end oflast year it was stated that for the previous six months thefloors of 25 schools in the county had been sprayed nightly witha liquid germicide, and the attendance compared with thatat a similar number of schools in which the process hadbeen omitted. The cost up to that date was R22 10s., andthe calculated increase of grants due to the additionalattendance in the disinfected schools, as compared with thenon-disinfected schools, amounted to fl.37 7s. 6d., a cleargain of fl.15 in favour of the disinfected schools. This pre-liminary report is undoubtedly very favourable.What I should like to see undertaken would be the treat-

ment of one group of schools by disinfectants and ofanother and similar group by spraying with water and

washing, thereby preventing the distribution of dust and

promoting the removal of dirt. Until -this is done we mustbe uncertain whether the diminution of infective disease, ifit occur, is due to disinfection or to general cleanliness, forundoubtedly in many schools systematic cleansing is almostunknown.17 I am informed by Mr. Marsh of the BucksEducation Committee that this method of control has beenadopted in their work, and I shall therefore await the pub-lication of the full report with very great interest. I have

recently had an opportunity of testing the bacterial contentof school dust. Five samples were untreated ; two sampleswere treated with a 1 in 400 solution of a well-known emulsifieddisinfectant. The results obtained were much the same forboth treated and untreated samples. Suspending 1 grammeof the dust in 100 cubic centimetres of sterile water and

making cultures with 1 to 3 loopfuls, bacillus coli and strepto-coccus fsecalis were not found. Working with largeramounts, 0’ 1 gramme to 1’ 0 gramme, bacillus coli andbacillus enteritidis sporogenes were found in all thesamples to approximately the same extent. If theseresults go for anything they do not suggest that dis-infection by sprinkling with a germicide has reallymuch effect on the bacteria contained in school dust.Disinfectant powders are extensively employed by the generalpublic, but unquestionably they have little value except asdeodorants. Any disinfecting action must be purely super-ficial and limited to the immediate surface on which thepowder lies. Carbolic powders are unpleasant and nauseatingto some individuals. Disinfectant powders have perhapsone thing in their favour. They tend to drive away flies andprevent them breeding in garbage and so diminish the fly

16 Journal of the Royal Army Medical Corps, April, 1908 (Dis-infection by Formaldehyde).

17 See Kenwood, Public Health, March, 1908, p. 8.

745

nuisance. The public should be educated to understand that ofthe chief value of a disinfectant powder is as a deodorant. act

I now pass on to the consideration of the disinfectants. he;The principal disinfectants comprise many metallic salts-in ini

particular those of mercury, the mineral acids, oxidising lik

agents such as ozone and peroxide of hydrogen, phenol and Hi

cresylic acid and their homologues, and various oxidised W:hydro-carbons. Many other substances are used as antiseptics tic

-e.g., boric acid and borates, salicylic acid, alcohol, salt, K<&c.-but have little germicidal power, and hence are hardly co

disinfectants in the proper sense of the word. The dis- in:infectants very frequently form compounds with proteins, and mion this property their germicidal power may largely depend ; us

they may form compounds with the bacterial proteins whichare incompatible with the life of the bacterial cells. Perhaps ne

all germicides have this power of combining with proteins, su

and heat, of course, causes coagulation of native proteins. 2.Since the time when the infective nature of certain nc

morbid products was first recognised, attempts have been shmade to ascertain the effect of heat and of disinfectants in la"destroying their infective properties. Between 1750 and ve

1752 Sir John Pringle reported experiments "for making pcstandards whereby to judge of the septic or antiseptic al

strength of bodies " and gave a table of the comparative en

powers of various salts in resisting putrefaction. Thus, sea on

salt being taken as unity (1) borax came out as 12 and alum pcas 30.18 One of the earliest attempts to ascertain the in

temperature at which infective matter loses its infectivity re

must be that of Dr. William Henry in 1832. He came to a

the conclusion that exposure to a temperature of 2000 F. for bEone hour destroyed the contagious matter of scarlet fever.Vaccine matter lost its activity after heating to 140&deg; F. for- three hours, but not after heating to 120&deg; F. for a similartime.19 Davaine 211 in 1873 investigated the temperature neces-sary to destroy the infectivity of anthrax blood. He foundthat a temperature of 550 C. disinfects in five minutes, atemperature of 500 C. disinfects in ten minutes, and a tem-perature of 48&deg; C. disinfects in 15 minutes. Roberts 21 alsoin 1874 showed that the destruction of putrefactive micro-organisms by heat might be accomplished either by a brief ex-posure to high temperatures or by more prolonged exposure tolower ones. Pasteur, similarly, having ascertained that variousfermentations are due to living organisms, proceeded to de-termine at what temperature these might be killed so thatthe keeping qualities of beer and wine might be prolonged, 1and introduced the system of pasteurisation so largely usedat the present day in the preparation of milk and othersubstances. Of British observers, Angus Smith, Calvert,Crookes, Parkes, and Dougall, and, I need hardly add,Lister, did valuable work in the middle of the last century.

In 1875 Buchanan Baxter carried out some careful experi- Fments on the germicidal value of certain disinfectants. Thiswas before the isolation of micro-organisms in pure culturehad been accomplished and Baxter therefore employedvaccine lymph, peritoneal fluid obtained from guinea-pigsdead from septic peritonitis, emulsion of glanders nodules,and "cultures" " of septic organisms obtained from putre- tfying material. The disinfectants tested were carbolic acid,sulphur dioxide, potassium permanganate, and chlorine. In 1the conclusions derived from the results of his work Baxternotes that : 22 (1) antiseptic is not synonymous with dis- 1

infectant power ; (2) the effectual disinfectant operation ofchlorine and potassium permanganate appears to depend farmore on the medium in which the infective particlesare distributed than on the specific characters of the ]particles themselves; (3) no virulent liquid can be con-sidered disinfected by carbolic acid unless it contain at least2 per cent. by weight of the pure acid ; (4) aerial disin-fection, as commonly practised in the sick-room, is eitheruseless or positively objectionable, owing to the false senseof security it is calculated to produce ; (5) when aerial dis-infection is resorted to the probability that the virulentparticles are shielded by an envelope of dried albuminousmatter should always be held before the mind; and (6) dryheat, when it can be applied, is probably the most efficient

18 See Del&eacute;pine, Journal of the Royal Institute of Public Health,vol. xvi., 1908, p. 579.

19 Philosophical Magazine and Annals, 1831 and 1832.20 Comptes Rendus, Sept. 29th, 1873.

21 Philosophical Transactions of the Royal Society of London, 1874,part ii.

22 Report of the Medical Officer of the Privy Council and LocalGovernment Board, New Series, No. VI., 1875, p. 216.

all disinfectants. But the desired temperature must bedually reached by every particle of matter included in theated space. Jalan de la Croix 23 in 1881 also studied thefluence of various media on the action of disinfectants and{ewise carried out experiments similar to those of Baxter.is work was of an exhaustive character and very valuable.’ith the advent of the isolation of bacteria in pure cultiva-on by methods which we owe primarily to the genius ofoch, a new era dawned whereby tests of greater accuracymid be made on the germicidal action and value of dis-Lfectants, and in nearly all the recent work on the deter-ination of germicidal power pure cultivations have beensed as the test objects.It may be of interest here to suggest the requirementscessary for an ideal chemical disinfectant. These may belmmarised as follows :-1. The substance must be cheap.It should be relatively non-poisonous. 3. It should haveo corrosive or other action on the ordinary metals and itiould not stain linen, &c. 4. It should not separate intoeyers on standing, and should run freely from the containingssel at all times. 5. It should possess high germicidalower. 6. It should be miscible with ordinary tap water inII proportions to form a stable solution or homogeneousmulsion which should not separate appreciably into layersn standing. 7. It may with advantage have a solventower for grease, for greasy surfaces have often to be dis-ifected. 8. Its germicidal power should not be markedlyeduced in the presence of organic matter. 9. Heating tomoderate temperature should not affect it, so that it may

e used hot if desired.

Three Bunterian LecturesON

THE MECHANISM UNDERLYING THEVARIOUS METHODS OF ARTIFICIAL

RESPIRATIONPRACTISED SINCE THE FOUNDATION OF THE

ROYAL HUMANE SOCIETY IN 1774.

Delivered in the Theatre of the Royal College of Surgeons ofEngland on March 1st, 3rd, and 5th, 1909,

BY ARTHUR KEITH, M.D. ABERD.,F.R.C.S. ENG.,

HUNTERIAN PROFESSOR AND CONSERVATOR OF MUSEUM, ROYAL COLLEGEOF SURGEONS OF ENGLAND.

LECTURE I.

Delivered on March 1st.

MR. PRESIDENT AND GENTLEMEN,-In order to make clearo you the circumstances which led to the foundation of the

oyal Humane Society I wish to carry you, in imagination,)ack to London of the year 1774. John Hunter was then iniis forty-sixth year, a surgeon at St. George’s Hospital, witht house in Jermyn-street, where he was collecting, teaching,md experimenting on an income of less than 91000 a year.Jlose by, in Windmill-street, his elder and successfulbrother William, with Cruickshank as his assistant, lecturedurilliantly to large classes. William Hewson, whose experi-nental ability equalled that of John Hunter, was establishedM a teacher and surgeon in Craven-street, Strand, havingquarrelled with, and separated from, William Hunter somethree years previously, in spite of the friendly negotiations oftheir mutual friend Benjamin Franklin. Anywhere betweenthe Temple and Leicester-square (then Leicester Fields) onemight have encountered Johnson, Reynolds, Goldsmith, orGarrick. The founder of the Humane Society, althoughknown to these four celebrities as well as to the Hunters, wasplain Dr. William Hawes, practising in Thames-street andphysician to the London and Surrey Dispensaries. In the yearof which I speak he was in his thirty-eighth year. He isknown to literary men as the friend and medical attendantof Oliver Goldsmith. By natural constitution he was an

23 Archiv f&uuml;r Experimentelle Pathologie und Pharmakologie, vol. xiii.,1881, p. 175.