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1371 Notes, Comments, and Abstracts. THE CONCEPT OF PREDISPOSITION BY JULIUS BARON, M.D. BUDAPEST. THE last decade may justly be called the period of renaissance of the theory of constitution and predisposition. A great deal has been done in a short time to substantiate the theory, but the practical results of these efforts are at present of little significance to the practitioner, because the ’ many new ideas are not clearly defined and so their application has led to faulty or contradictory results. On the other hand, little would be gained by their exact definition, for concepts can only be accurately defined when their content has been clearly set out. The definition is just the summary of the analyses of the concept in question, and a very large number of analyses are still necessary in order accurately to define constitution and predisposition. The present paper is a contribution to this work. The Accepted View. As a starting-point let us choose a statement to criticise. This statement has not been made elsewhere, at any rate in its present form, but it can be regarded as the generally accepted view of predisposition. " Two healthy individuals are exposed to the same external conditions and one falls ill, while the other does not. We say that the sick person has a greater predisposition to the malady than the healthy one." On analysing this statement, our attention is arrested by the expression " to the same external conditions." It is obvious that no two individuals can be exposed to the same conditions in a mathematical sense. Let us, however, regard it as possible, and then disregard the conditions which we do not consider important for the development of the illness. Which these are we must decide on the basis of experience. The train of thought is somewhat as follows : We know from experience that, as a rule, no more persons fall ill of typhoid on a Tuesday than on a Friday-so that the day of the week is of no importance in the onset of the disease. Therefore experience can influence our results in comparing the predisposition of two individuals to the same malady. An alteration in our experience can, in the same way, bring about a change in the result of the comparison. The expressions " remaining well " and " falling ill " must also be examined more closely. It is a constantly reiterated fact that there is no strict line of demarcation between " being ill " and " being well." Such a line can only be arbitrary. The following possibilities remain. The boundary between illness and health can, for a given disease, be drawn arbitrarily in two places ; if it is drawn in the first A remains well while B falls ill, and if it is drawn in the second B remains well and A falls ill. The arbitrary boundary between health and sickness is, therefore, the . deciding factor in comparing the predisposition of the two individuals. We must consider also another possibility. A and B are exposed to the same external conditions, which we will call Kl’ A is taken ill and B remains well, so that the predisposition to the disease is greater in A than in B. Let us assume that A and B are exposed to the conditions K2 and B falls ill while A remains well. If the view of predisposition is to retain the meaning described in our statement, we must assume that such contradictory condi- tions as Ei and K2 are not possible. The possibility of such conditions is, however, quite an open question, and we even regard it as very probable. A Mecharaical Analogy. Finally, let us discuss whether we are justified, when investigating the cause of an illness, in separating the external conditions from the predisposition, " internal conditions," and setting them in opposition to one another. We can throw some light on this question by an analogy. Instead of a healthy individual, let us examine a well-defined mechanical system. As analogies for illness and health let us admit two well-defined possibilities of alteration in the system under certain external conditions. As both external and internal conditions can be easily reviewed the conception of predisposition can be studied especially well in this case. Let us imagine a homogeneous, accurately proportioned and rigid die, with three sides painted white and three black. We place the die accurately on a certain point of a strong spring and, having compressed the latter to a given degree, release it in a prearranged manner so that the die falls on a relatively large, rigid, and perfectly horizontal surface. There are two possibilities ; the uppermost surface of the die is either white or black. If we repeat the experiment frequently under the same conditions we can easily convince ourselves that the possibilities of the two cases are equal. We cannot foretell the result of any one experiment, even with our knowledge of the various internal and external conditions. If we take two absolutely similar dice, and assume that in an experiment the one shows black and the other white, we must assume, according to our hypothesis, a greater predisposition for black in the first die and a corresponding predisposition for white in the second. It is clear that, in this case, the conception of predisposition has been wrongly applied. If we reflect how it is possible for the experiment to lead to various results, under the same external and internal conditions, then we see that the mistake lies in the abstract conception of " the same conditions." In this case we cannot know whether some apparently quite insignificant factor did not have a decisive influence on the result. Mathematically speaking, identical conditions cannot be produced, and the result varies according to numerous extremely insignificant variations which we neglect in reproducing " the same conditions " and which, even when they can be easily studied, can never be calculated. They are summarised in the concept of " chance." Let us now imagine that inside the die, near one of the white surfaces and opposite a black surface, is a small body of great density. This transfers the centre of gravity from the geometrical centre towards the white surface. In this case a " black " results more frequently than a " white," and one can logically assert that the die is more predisposed to " black " than to "white" and has a greater predisposition to " black " than the first die. Yet it is very possible that if one experiment only is made with both dice the die with black " predisposition might turn up white, and vice versa. i We have confined ourselves so far to a system of which the internal conditions have remained unchanged throughout the experiments. The patient who has convalesced, on the other hand, often shows an altered predisposition to the disease. In order, therefore, to complete our analogy, let us imagine that part of the interior of the die is semi-liquid and that the small body is suspended in this part, but is not moved by gravity alone. Now, the centre of gravity alters its position during the course of a single experiment. If we look at the die from the outside only we cannot determine its predisposition, even by experiment. If we assume that the position of the heavy body only alters markedly after the completion of the experiment, then we can express an opinion on the predisposition of the die, but only after an autopsy (i.e., opening the die or X raying it) can we be sure of our statements. Given a number of such dice, in which the small heavy body can take up any position, and excluding autopsy, one could only speak of a predisposition if certain external easily determinable qualities were present in combination with definite types of predisposition. The occurrence of such combinations could be determined along statistical lines. Conclusion8. One can only speak of a greater or lesser predisposition to a given illness when definite, easily determinable qualities occur in conjunction with a greater or lesser frequency of the illness, the qualities being determinable either through the experience that they are necessary or merely by statistical methods. Given the same external conditions, the assumption of a greater predisposition on the part of the sick person only leads to a confusion of the idea of predisposition. PERIODICITY IN DISEASE PREVALENCE. AT a meeting of the Royal Statistical Society held on Dec. 18th Mr. H. E. Soper, of the National Institute for Medical Research, discussed the interpretation of periodicity in disease prevalence. The fact that epidemic diseases often come upon us in the manner of surges, attended with great inconvenience and fraught with many special dangers when at their height, should be sufficient incentive, he thought, for a close study of the fluctuations in disease prevalence, and many attempts to account for the periodic nature of the visitations of sickness have from time to time been made. Amongst the various theories put forward to account for epidemic recurrence, perhaps the most favoured theory presents a picture of a rise and fall in the new cases of a contagious disease as consequent upon a glut and dearth of susceptible persons ; for, clearly, if there is a limit to the numbers who can contract the disease, the action may be supposed to go after the manner of a pendulum, where, as the energy of flow becomes exhausted, the energy of potential activity gets stored up, to be released again when motion recommences. The stored energy is the accumulation of susceptible children, by birth. By means of arithmetic and algebra a simple supposition in regard to the delayed or lapsing infectivity of an infected person, combined with a supposition of a constant inflow by birth of susceptible children, can be shown to lead to an ever- sustained periodic wave, or swing of the epidemic pendulum, whose period could be interpreted. These idealised waves do not, however, give a very true replica of the curve of
