Comparative immunology in pediatrics (paper written by Dr. James D. Trask in 1928).

In pediatric clinics interest is conventionally centered about problems peculiar to infancy or childhood. Obviously this point of view is necessary for the adequate care of patients and it has been the stimulus for many important studies. A more liberal view could perhaps be taken in the case of certain specific infectious diseases which occur throughout life, and which exhibit varying clinical features that can be correlated with age. Comparative anatomy magnifies the appearance and disappearance of organs that are recognized and then lost in embryonic development; similarly comparative immunology might show recognized phenomena more clearly or even make possible the formulation of new biologic principles. It was on the basis of comparative immunology that Metchnikoff founded the school of cellular immunity. The fantastic advocacy of this, against the humoral school, developed our present knowledge of anti-microbial defense. Metchnikoff wrote [1], "At a period when medical men and veterinary surgeons were content to record the presence of Bacteria in the blood of their patients without attributing to them the slightest etiologic role, botanists and zoologists had already proved most definitely that many plants were subjected to epidemic diseases, undoubtedly set up by the parasitism of various exceedingly simple organisms." It is not clear that Metchnikoffs technic of investigation-a method of comparative study-has ever been applied in the clinic. At any rate it has not thus been employed in the past ten or fifteen years during which time the general concept of anaphylaxis has been extended, ideas of serologic specificity and of bacterial mutation and virulence have been consolidated, notions about the mechanism of disease have been formulated, and bacterial antigens have been obtained as pure chemicals. With the newer knowledge concerning the variability of the parasite one should reconsider variability of the host. In the infectious disease clinic one could make use of the method of comparative immunology by applying a bacteriologic or immunologic technic to measure a feature of disease, the results to be correlated with age. As a case in point let us consider the specific toxemias, taking scarlet fever as an example because there is considerable data on the toxic aspect of the disease. These facts can be applied from the point of view under discussion, namely, that of comparative immunology. The test, devised by Dick and Dick [2], for susceptibility to the disease is carried out by inoculating intracutaneously a standard amount of scarlet fever toxin. If a local redness develops during the next day, the test is positive; if it does not, the result is negative. A positive test is supposed to indicate that the individual possesses