381l JUBILEE NUMBER.

BOVINE TUBERCULOSIS AND ITS CONTROL

Editorial Articles written for this Journal (Vol. 12) by Professor J. M'Fadyean in theyear 1899, i.e., Seventeen years after the publication of Koch's discovery of the Tubercle

Bacillus, i.e., in 1882.

THE STAMPING OUT OF TUBERCULOSIS.As time advances, and information regarding the prevalence of the disease isaccumulated, the difficulty, not to say the impossibility, of eradicating tuberculosisfrom among the domesticated cattle of this country becomes more and more apparent.The difficulty of diagnosis, which before the discovery of tuberculin [1890], stoodas an insuperable barrier to stamping-out measures, has now almost entirely dis­appeared, but a new and equally great obstacle has been brought to light in thediscovery that about one-third of the adult animals of the bovine species in GreatBritain are already affected with tuberculosis. In support of this estimate, it may bementioned that during the past two years particulars relating to the testing of 4,379cattle have been communicated to the Editor by members of the veterinary professionpractising in various parts of England and Scotland, and that out of that number1,389, or 31·7 per cent., reacted. As with few exceptions the animals tested wereapparently healthy, there does not appear to be any ground for believing that if thewhole of the breeding cattle in the country were tested the proportion of them foundto be affected would be much less.

The discovery that about one-third of the breeding stock of the country arealready affected with tuberculosis has made it impossible for any sane person to main­tain that the Board of Agriculture ought to schedule tuberculosis under the Diseasesof Animals' Act, and proceed to apply to it the measures which were successful instamping out cattle plague and foot-and-mouth disease, but plans which are scarcelymore rational are being urged upon the Government by some of their irresponsibleadvisers. An example of these crude, ill-considered schemes is furnished in a paperby Mr. Hunting which appears in a recent number of the Journal of the Society of theArts.*

Mr. Hunting recognises that if 20 per cent. of our adult cattle. are infected, andwe assume that all these animals must be slaughtered and partially paid for, "weenter on an undertaking that neither the owner of stock nor the taxpayer wouldapprove." But he thinks" there is no necessity for such wholesale slaughter," andhe proceeds to unfold the following plan for dealing with the disease.

" The majority of infected cattle are not infective to others-they are neitherdangerous to man nor other animals, and their slaughter would be a wicked waste.Only the visibly affected are dangerous, and their number does not exceed 40,000.This estimate would include every animal whose carcase is wholly unfit for humanfood and every cow whose milk is unfit for consumption.

"The slaughter of these would be a loss to the owners, but it would be a publicbenefit, and it is expedient and just that the public should share the loss.

" I suggest that Local Authorities should pay as compensation £2 per head forall compulsorily slaughtered of a value not exceeding £8; and a Supl equal to one­fourth the market value of all others seized-but no animal should be valued at over£24. Any salvage on carcases, minus the cost of removal and slaughter should berepaid to the owner.

" The payment of £2 as compensation for miserable animals that are a dangerto man or to other stock may seem an illogical proceeding, but unless some suchinducement is offered, many of them would be sold to the lowest class of butcherand find their way into human food. A payment of £2 per head would make itworth the while of the owner not to evade reporting to the authorities, and so theexistence of disease would become known with greater expedition. Infected premisesonce recognised could be supervised in such a way as to assist the owner and protectthe public.

" Compensation at the rate of £2 for all animals below the value of £8, and com­pensation at a higher rate on all over that value would probably reach a cost of£100,000 in the first year and a constantly decreasing sum every year afterwards untilno disease existed. This is less than is now paid every year for the attempts to stampout swine fever.

"For this payment what should we receive? A guarantee against humaninfection from animals, and a gradual but rapid suppression of disease amongstock."

*January 27th, 1899.

BOVINE TUBERCULOSIS ANO ITS CONTROL 387

It is doubtful whether anyone aspiring to guide public opinion on the tuberculosisquestion has ever offered such ill-judged advice, or made a forecast which is soabsolutely unjustified by knowledge and experience. Here we are told that onlyvisibly tuberculous animals are dangerous, and that the slaughter of such animals,coupled with compensation to their owners, would lead to a rapid suppression of thedisease. Furthermore, that the money required for compensation would probablybe £100,000 during the first year, and less each succeeding year" until no diseaseexisted." Now, if there is one well-ascertained point in connection with the subjectof tuberculosis among cattle, it is that the disease cannot be stamped out by the simpleand comparatively inexpensive method of slaughtering the animals that developclinical symptoms of the disease. The idea to the contrary is so obviously erroneousthat an apology is almost necessary for taking the trouble to refute it.

Mr. Hunting estimates that in the course of a year only 40,000 animals wouldrequire to be slaughtered on account of external indications of tuberculosis, and this,calculated on the basis of the most recent returns of the number of cattle in theUnited Kingdom, represents one animal for every 126 of the cattle population.Otherwise stated, Mr. Hunting supposes that tuberculosis could be rapidly suppressedby the slaughter, on an average, of one animal annually in every third or fourthlot of cattle in the country, for the average number of animals in the possession ofthe same owner probably does not exceed 40. One is prompted to wonder why,if the matter is so simple as this, there is any call for the intervention of the State,at least, so far as the interests of cattle-owners are concerned. Alas, that it shouldnot be true that only every third or fourth farmer or cowkeeper in this country hasin the course of a year as much as one clinically tuberculous animal.

One is tempted to think that some people spend so much of their time in theexcogitation of what may be termed fancy methods of dealing with tuberculosisthat they have no time to look into the recorded experience of those who have beenpractically applying themselves to the eradication of the disease. Hundreds offarmers and veterinary surgeons can testify to the practical impossibility of stampingout tuberculosis from among housed cattle by the slaughter of the visibly affected,and tuberculin has revealed to many an astonished owner that 20 or 30 per cent.of his animals are tuberculous although for years previously he had not lost a singleanimal from the disease, or had any reason to suspect its existence in his herd. Nordoes this by any means state the full measure of the difficulty of stamping out tuber­culosis. Centuries of the operations recommended by Mr. Hunting would notsuffice to stamp out tuberculosis, and even when resort is had to tuberculin, and everyanimal that reacts is killed or isolated, a clean bill of health is not always immediatelyobtainable. If anyone doubts this, he may be referred to the often-cited experimentsof Professor Bang in Denmark. Take, for example, the results of the attemptsto eradicate the disease from the farm of Thurebylille. Here the whole herdwas first tested in the spring of 1892, and all the animals that reacted-not merelythe visibly diseased, as in Mr. Hunting's plan-were promptly removed to a separatecompartment. Twice annually after that, for 5 years, the tuberculin test was appliedto what was called the " sound section," and on each occasion any animals thatreacted were removed. What was the result? The eighth, ninth, and tenth testsrevealed respeetively seven, seven, and six cases of tuberculosis; in other words.iJ years of this system had not sufficed to eradicate the disease. In face of this experi­ence, how can anyone with a reputation to lose pretend that tuberculosis could bestamped out by merely killing the visibly diseased animals?

To tell farmers that " only the visibly affected are dangerous," is to seek topropagate a most dangerous error. What requires to be impressed upon them isthat the disease may be spread by an animal that appears to be perfectly healthy,and that, therefore, every animal that reacts to tuberculin must be considereddangerous, if the object is to obtain a clean bill of health.

But it may be said that if ten applications of the tuberculin test at half-yearlyintervals to the apparently healthy animals, followed on each occasion by the removalof those that react, will not eradicate the disease, the ultimate advantage would notcounterbalance the trouble and expense. It is probable, however, that the objectin view may be obtained in much less -than 5 years. As indicated elsewhere in thisnumber, the tuberculin test is not infallible, and to guard against the possibilitiesof error, it ought to be repeated at shorter intervals than 6 months, at least, during thefirst year.

We do not agree with Mr. Hunting in thinking that tuberculosis can be stampedout by the slaughter of the visibly diseased animals, but for another reason we considerthat it is time that the law took cognisance of clinical symptoms of tuberculosis incattle. In the forefront of such symptoms stands tuberculous disease of the udder.

388 JUBILEE NUMBER.

Sinct: our last issue the Local Government Board have issued an order amendingArticle 15 of the Dairies, Cowsheds and Milkshops Order of 1885, so as to providethat for the purposes of paragraph (a) and (b) of that Article reference to diseaseshall include, in the case of a cow, such disease of the udder as shall be certified bya veterinary surgeon to be tubercular. This is no doubt a step in the right direction,hut it is a very halting and inadequate step, since in the case of large towns whichdraw their milk supply mainly from outside sources it will leave the dangers arisingfrom the sale of milk from tuberculous udders practically untouched. Tuberculousdisease of the udder, or, better still, every disease of the udder of a milch cow. ought tobe made notifiable. and the sale of milk from a diseased udder ought to be forbiddenunder a penalty. For reasons which we have explained in former articles. we are alsoof opinion that the sale of milk from an animal that is obviously tuberculous in anypart of the body should be prohibited, and that notification of obvious signs oftuberculosis in a milch cow ought to be made compulsory. These measures arenecessary as reasonable safeguards to the milk-consuming public, though theirintroduction cannot be urged on the ground that they would ever suffice to stamp outtuberculosis.

IS THE TUBERCULIN TEST INFALLIBLE?

"Is the tuberculin test infallible?" is one of the questions frequently askedby those who contemplate having their cattle tested. If the answer has to bemonosyllabic it must be" No." No agent in human hands can be said to be infalliblefor any purpose, and although with the exercise of proper precautions the tuberculintest is marvellously reliable. it is not absolutely free from the chance of error, as thefollowing considerations will show.

In the first place, tuberculin is not a substance of definite chemical compositionand strength. It is obtained by cultivating tubercle bacilli in an artificial nutrientliquid, and its efficacy as a test depends upon certain substances of ill-defined chemicalcomposition which are added to the liquid by the vital activity of the bacilli growingin it. As regards their mode of origin, these substances may be compared to thealcohol which is formed in a saccharine solution in which one of the yeasts is cultivated.Tuberculin would be termed weak or strong according to its richness in these sub­stances, and it is a test for tuberculosis because a quantity of it which producesno appreciable effect on a non-tuberculous animal excites a short but sharp attack offever, manifested mainly by a rise of temperature, in one that is tuberculous. Butby using a sufficiently large quantity of tuberculin one may cause the temperatureto rise in an animal that is free from tuberculosis, and by using too small a dose oftuberculin, or a tuberculin that from some error in its manufacture is too weak. onemay fail to cause an elevation of temperature even in a tuberculous animal.

These facts alone may appear to carry with them serious chances of error, but asa matter of fact. the risks of miscarriage which they involve are inconsiderable.provided the tuberculin is obtained from some reliable source. for there is alreadya large experience to guide those who manufacture it as to the proper dose, and thereis fortunately a wide margin between the quantity that will excite a reaction in atuberculous animal and the quantity that will cause the temperature to rise in a healthyone.

Another possibility of error arises from the fact that one has to measure thereaction to tuberculin by the elevation of the animal's temperature during the Ii)or 18 hours after the injection of the substance, and that during this period tht:temperature may rise from some cause quite unconnected with the injection oftuberculin. This, again, may at first sight appear to provide serious risk of errorsin diagnosis. but there is a circumstance which reduces it to very small proportions,Tiz., the fact that the reaction to tuberculin is measured not entirely by the amountof the elevation of temperature, but also by the manner in which the temperatureascends. The normal temperature of the ox is from 101 0 to 1020 F .• and when atuberculous animal of that species is tested with tuberculin its temperature beginsto ascend a few hours afterwards, and gradually rises two. three or four degrees. themaximum point being reached about the 12th or 15th hour, after which it graduallyfalls again to the normal. Every rise which has this character must be taken as anindication that the animal is tuberculous, but sudden ascents of temperature followedhv sudden falls to the normal must be set down to some accidental disturbance.The subjoined temperatures of two animals under the test will make this plain. thefirst showing the gradual ascent of a tuberculous animal, and the second an erraticrise determined by an accidental disturbance.

BOVINE TUBERCULOSIS AND ITS CONTROL. 389

,Vo. T£me of Ttlject£oll. 3 Hours. 6 Hours. n Hours. 12 Hours. ]5 Hours.

10]'8 ' 102·4" ]03·4° 106·6 . 105·8" 105·2"2 102" 10] .(f~ 102·2~ LOl·T 101·7° 105·8°

] t will thus be seen that one is able to recognise a good many accident~1 rises oftemperature in animals under the test, and thereby to avoid the mistake of classingthe animals in question as tuberculous, but it must be confessed that no amount ofcare can altogether evade the chances of error from this cause, and in certain circum­stances these become very considerable. That is notably the case in animals that havebeen exposed before 01' during the test to excitement, such as is occasioned by transport­ing them to strange. surroundings. On this account it has already been abundantlyproved that the test is not to be relied upon when carried out on cattle in a marketor slaughter-house. \Vherever possible, cattle should always be tested in their ownpremises, and if they have experienced a change of quarters, the operation oughtto be postponed until observation with the thermometer has shown that the tempera­ture has become quite normal and steady. The complaints regarding uncertaintyand errors in the application of the test to valuable animals sold for export areprobably ascribable to neglect of this very necessary precaution.

The foregoing are possibilities of error in the direction of diagnosing tuberculosisin healthy animals, which is probably regarded by most people as the most objection­able mistake that can be made in carrying out the tuberculin test, but there is alsoa chance of error of the opposite kind, that is to say, of passing a tl\berculous animalas healthy. Obviously this is a very unfortunate mistake to make, for it may lead tothe introduction of the disease into a previously healthy herd, or it may nullify thesacrifice which an owner has made in disposing of all the animals that have reacted,with the object of eradicating the disease from his stock.

Mistakes of this kind probably sometimes arise from an oversight in performingthe operation, part or whole of the dose of tuberculin escaping between the hypodermicneedle and the nozzle of the syringe, perhaps owing to some sudden movement of theanimal at the moment of injection. Obviously, with the exercise of proper care, thisought to be a very rare accident. There is, however, one chance of error in thisdirection which is less easily avoided. It appears to be a very well established fact thatan animal with actual tuberculous lesions in it will react to tuberculin, but between themoment of infection and the formation of actual lesions in the part to which thebacilli have gained access-the lungs for example-a certain time must elapse.Infection with the bacilli, whether by inhalation or ingestion, may be momentary,but it is not credible that an animal infected in the forenoon would react in theafternoon of the same day. The period of time that must elapse after infection'before a reaction can be obtained is as yet undertermined, and possibly it variesaccording to the method of infection. The point is one of considerable importance,and the following experiments bear upon it. A steer which gave no reaction totuberculin was infected by the injection of living virulent tubercle bacilli into one ofits veins. Nine days afterwards, when tested with tuberculin, its temperaturegraduallv rose from 101·4° until at the twelfth hour it had reached lOG·iI', after whichit gradUlilly declined. A heifer which did not react was infected in the same manner,and when re-tested 8 days afterwards it displayed a typical reaction, the temperaturerising gradually to ] Ofi C

• The test was repeated 10 days later, and with a similarresult.

It ought to be observed that in these cases a large number of bacil]i were usedto infect the animals, and it probably would not be safe to conclude that a reactionwould be obtained as soon after natural infection bv the inhalation of a few bacilli.To counteract this source of error it is advisable, when an attempt is being made toweed the disease out of a herd, to re-test,those which have not reacted on the firstoccasion after an interval of not more than ;{ months.

Lastly, among the possible errors that may be made in using tuberculin, theremust be included the occasional failure to elicit a distinct reaction in animals whichare emaciated and near the point of death from tuberculosis. This, however, cannot beconsidered a serious defect in the use of tuberculin, for such failures are only met within animals that are worthless, and whose tuberculous condition is almost obvious.

It will be seen from the foregoing considerations that the tuberculin test is not onein which the possibility of error is absolutely excluded, but when the sources of errorare known beforehand they may be guarded against, and a most trustworthy indica­tion as to the existence or non-existence of tuberculous disease in the animal testedmay be obtained.

M

390 JUBILEE NUMBER.

VETERINARY INSPECTION OF MILCH COWS.THE recent Order of the Local Government Board giving Public Health Authori­ties power to prohibit the sale of milk from cows affected with tuberculous diseaseof the udder has given fresh importance to the question of veterinary inspectionof dairies and the means by which tuberculous mastitis may be diagnosed in theliving animal. It is gratifying to learn that in several boroughs arrangements for aperiodic inspection of all the dairy cows within the boundaries by a qualified veterinarysurgeon have already been made, with a view to the detection and elimination of casesof tuberculous disease of the udder. This is, no doubt, a step far short of whatmany people have demanded, and we have already expressed the opinion that moreextended powers are necessary to enable large towns which draw their milk supplymainly from outside sources to prevent the sale of unwholesome milk. Nevertheless.if full advantage is taken of the new Order the sale of milk from cows affected withmammary tuberculosis may be made much more difficult than it has been hitherto.

The first question which arises in connection with the exercise of the powersconferred by the new Order is, how frequently is it necessary to have the udders ofmilch cows inspected in order to guard against the sale of tuberculous milk? Thisis a question not easy to answer. It may safely be asserted that the shorter the intervalsbetween the inspections the better, but a limit to the frequency of inspection is placedby the expense thereby incurred. On this account it would be useless to recommendinspection at shorter intervals than a fortnight, and at first many authorities willprobably be content with less frequent examinations, but if any substantial benefit is tobe obtained from the exercise of the powers conferred by the Order the intervalbetween the inspections should certainly not exceed one month. In this connection,it must be remembered that no obligation to report cases of tuberculous diseaseof the udder is laid upon the owner of cows, and that no penalty for the sale of tuber­culous milk can be inflicted so long as the sale has not been prohibited on the certificateof a veterinary inspector to the effect that the animal in question is affected withtuberculous disease of the udder. Had notification been made compulsory, and thesale of milk from a cow with a visibly diseased udder been forbidden under a penalty,there would have been less occasion to insist upon a frequent veterinary inspection ofdairy cows.

The second question arising out of the new Order relates to the means by whichtuberculous disease of the cow's udder may be diagnosed while the animal is stillalive. According to our present knowledge the characters which serve broadly todistinguish tuberculous mastitis from other diseased conditions of the udder are:(1) that it is always insidious in its onset, (2) that its course is always chronic, (3) thatit never ends in resolution, (4) that it steadily adds to the volume and density of theinvaded quarter, and (5) that at the outset of an attack the milk is not notably alteredeither in quantity or appearance.

It has been stated that tuberculous disease of the udder has sometimes a com­paratively sudden development, and a semi-acute course. This is probably an errorif it implies that a previously healthy gland may within a few days develop a tuber­culous lesion so gross as to be readily detected by manipulation. There is no reasonto suppose that tuberculous disease proceeds with much greater rapidity in the udderthan in other organs such as the lung or a lymphatic gland, and both natural andexperimental cases teach that a period of weeks rather than days elapses between theinfection of an organ and the development of macroscopic lesions in it.

The insidious onset of tuberculous mastitis is a character valuable for diagnosis,and at the same time one which renders the disease peculiarly dangerous. Wben areliable clinical history is obtainable to the effect that within the course of a day ortwo a previously healthy quarter has become considerably enlarged, and when thisenlargement is associated with the usual signs of acute inflammation-an abnormallyhigh surface temperature, congestion of the superficial vessels, and tenderness onpressure-it may safely be concluded that the lesion is not of a tuberculous nature.By this means a great many cases of udder disease can immediately be dismissedwhen only tuberculous mastitis is being sought for.

The commonly occurring non-tuberculous cases of mastitis develop rapidlywith the before-mentioned accompaniments of acute inflammation, and in the greatmajority of such cases the affected quarter begins to shrink as the acute inflammatoryphenomena subside. This is also a very valuable point for diagnosis, and it enablesone to put aside all those cases in which a cow has only three active quarters, with afourth which vields little or no milk and is abnormallv small in size. On the otherhand, a quarter that is larger than its fellow of the' opposite side, and induratedwithout tenderness, must always be provisionally diagnosed as tuberculous.

Stress has, by some authors, been laid on the condition of the supramammary

BOVINE TUBERCULOSIS AND ITS CONTROL. 391

lymphatic glands as a guid" to diagnosis, but, as a rul", in actual practice, v"ry littleinformation is derivable from that source. In the early stages of lactation in cows withlarge fleshy udders, it is often quite impossible to ascertain the conditions of the glands,and they may escape detection even when they are considerably enlarged. Besidesthat, the glands are generally more or less enlarged in all forms of inflammation of theudder, at least, while the disease is in an active stage.

A less constant character of tuberculosis of the udder than those previously notedis invasion of the quarter from above downwards. The great majority of acuteinflammations of the gland begin around the milk cistern, at the lower part of thequarter, but the whole quarter speedily becomes involved, and at the time whensuch cases come under observation it is impossible to trace how the disease began.On the other hand, one often encounters cases of tuberculous mastitis with markedenlargement and induration at the upper part of the quarter while a portion of thegland over the base of the teat is still of the normal size and flaccidity. It is true,however, that tuberculous disease of the udder sometimes appears to begin at the lowerpart of the quarter.

The character of the induration in tuberculous mastitis deserves special attention.The nodular character of tuberculous lesions in the other organs commonly affected,such as the lungs, liver, and serous membranes, is apt to lead one to expect a similarcondition in tuberculosis of the udder. As a matter of fact, however, the diseasein the udder is seldom tuberculous in the anatomical sense, for instead of a number ofwell-defined nodules or tubercles embedded in comparatively sound gland tissue,one usually finds a single diffuse indurated area shading gradually into the surroundingflaccid tissue of the udder.

A negative characteristic of tuberculosis of the udder which is of some value fordiagnosis is that the lesion has little or no tendency to soften, and seldom or neverbursts spontaneously through the skin. On the contrary, the lesion generallybecomes firmer with age, and sometimes acquires an almost stony hardness fromcalcification.

In the generality of non-tuberculous inflammations of the udder, and alwaysin those of an acute character, the milk is from the outset profoundly altered incharacter and amount. It is usually purulent, curdy, or ropy in consistence, andfrequently it is more or less deeply tinged with blood. The amount of secretionthat can be drawn off through the teat is always diminished. In tuberculosis of theudder, on the other hand, the lacteal secretion may not be sensibly altered in appear­ance or quantity at a time when the lesion has attained considerable dimensionsand is easily detectable by manipulation. In the later stages, however, when tbegreater part of the quarter has become involved in the disease, the secretion is greatlydiminished in amount and quite abnormal in appearance. Such liquid as can thenbe drawn off is generally whey-like in colour, and on standing it deposits a considerableamount of sediment. It ought to be observed, however, that similar appearancesmay be presented by the milk in the late stages of the acute non-tuberculous inflamma­tions.

ProbablY the most constant of the characteristics of tuberculous disease of theudder is the presence of tubercle bacilli in the milk of the affected quarter. Unfor­tunately, this character is of less value for clinical diagnosis than it might at firstsight appear to be. It is only exceptionally that the bacilli occur in the milk in suchnumbers as to make it practically impossible to overlook their presence when aproperly prepared cover-glass preparation is examined with a suitable microscope,and if it were made a rule that the disease must not be diagnosed except when tuberclebacilli can be demonstrated microscopically in the milk condemnation would in manycases have to be dangerously delayed. Nevertheless, in every case in which the clinicalcharacters of the udder disease raise a suspicion of the lesion being tuberculousthe milk ought to be microscopically examined. Ought such examination to beundertaken by the veterinary surgeon? The answer to that is that there is no,'eason why he should not, provided he has hy practice assured himself of his ahilit\·to detect tubercle bacilli in any product in which they are present in considerablenumbers. He must be equipped with a good bacteriological microscope, comprisingan oil-immersion lens, and magnifying SOO diameters. Any slaughter-house willprovide him with abundance of material on which he may exercise himself in stainingtubercle bacilli by the Ziehl-Nielsen or other approved method, and detecting themwith the microscope. When he has confidently mastered the technique of thisprocess, he need not hesitate to apply the same methods to the discovery of tuberclebacilli in milk.

During the advanced stage of tuberculous mastitis, ,vhen the m.ilk has becomemarkedly altered in appearance, a competent person will seldom fail to detect the

392 JUBILEE NUMBER.

bacilli in the first few cover-glass preparations examined. At this stage, the milkon standing generally deposits a considerable amount of sediment rich in leucocytesand other cells from the udder, and this is the material that ought to be selected formiscroscopic examination.

As long as the milk furnished by the suspected quarter is comparatively normalin appearance and quantity it is a great advantage to have a small centrifugal machine,by means of which the cream may quickly be obtained from a sample of milk and anysolid particles in it that tend to precipitate may with equal rapidity be thrown down.It has been stated by some observers that in centrifugalised or separated milk thebacilli are mainly or entirely found in the thin milk or in the sediment. This iscertainly not the case when the milk is still normal in appearance and fairly richin cream, for the bacilli are then carried up in considerable numbers with the milkglobules, and are often more readily found in the cream than in the remainder of thesample. Probably the safest plan is to stain preparations from both the cream and thesediment. In the absence of a centrifugal machine, the sample of milk to beexamined may be allowed to stand for 12 hours or more in a conical glass vessel untilthe cream has risen and any splid particles have fallen to the bottom.

When tubercle bacilli are found in milk that has been taken with precautionsthat exclude the risk of accidental infection no room is left for doubt as to the diseasedcondition of the udder, but it must not for a moment be supposed that failure to detecttubercle bacilli with the microscope, even when the search has been a prolonged one,justifies one in concluding that the udder is not tuberculous, or that tubercle bacilliare not present in the milk. One may add tubercle bacilli to milk and then diluteit to such a degree as to make the detection of the bacilli in it with the microscopealmost impossible except by spending an unreasonable amount of time in the search.Nevertheless, such diluted milk remains infective if used in sufficient quantity,and although the danger is no doubt le;:ss in proportion to the degree of dilution,one cannot admit that milk is fit for human food when it contains onlv a few tuberclebacilli. '.

The considerations just referred to raise an important question, viz., what isthe duty of a veterinary inspector entrusted with the powers conferred by the recentOrder of the Local Government Board when in the case of a cow with an enlarged,indurated, and painless quarter he is unable to demonstrate the presence of tuberclebacilli in the milk.? We think that he ought not to hesitate to diagnose tuberculosisof the udder in such circumstances, and by so doing give the human consumer ofthe milk, rather than the cow, the benefit of the doubt. In such a case, however,the diagnosis and the suspension of the milk may be made provisional, until the cowcan be tested with tuberculin, or until the milk can be tested by experimental inocula­tion. It may be objected that the tuberculin test cannot be employed to determinewhether a given lesion of the udder is tuberculous or not, since a reaction merelyindicates that there is tuberculous disease in some part of the animal's body. Inspite, however, of the force which lies in this objection, it is worth while to employthe test in doubtful cases of this kind, for, in the first place, it may show that theanimal is not tuberculous anywhere, and thus remove the suspicion that attachedto the udder, and, in the second place, in the event of a reaction being obtained ina cow whose udder is clinically tuberculous, the fact must be allowed some weightin considering whether the animal ought to be condemned for milk purposes.

In all cases that remain doubtful after clinical and microscopical examination,inpculation experiments may be employed, the use of the milk being in the meantimesuspended. This is beyond any doubt the most delicate test for the presence oftubercle bacilli in milk, but little need be said with regard to it here, since experimentsof this kind are illegal on the part of those who do not possess a vivisection licence,and because for their successful employment facilities which are not usually at thecommand of the ordinary practitioner are required.

There is, however, one point connected with the testing of milk by inoculationexperiments to which it is fitting to call attention here-namely, the necessity ofcollecting the sample to be tested in such a way as will avert the chance of error fromaccidental contamination of the milk with tubercle bacilli after it has left the cow'sudder. With this object it is necessary to cleanse and disinfect the teat and the handused for milking, and to collect the milk in a clean, sterile bottle. In this connection,it may be observed that when milk taken as it leaves the farm or dairy is found tobe infective bv the delicate test of experimental itlOculation, it does not follow thatthe herd of co\-.·s furnishing the milk in question contains an animal with tuberculousdisease of the udder. The sediment which common market milk too frequentlvdeposits on standing is mainly composed of excrement and other dirt from the cow'sudder or from the air of the cowshed, and matter of that kind derived from premisescontaining a large proportion of tuberculous cows may add tubercle bacilli to milkthat is quite wholesome as it leaves the gland.