Each year the papers written on allergy cover a wider territory. What the study of allergy cannot do is being separated little by little from what it can do, and the correlation of such study with internal medicine is improving all the time. Whereas tests for allergy appear to offer a distinct and separate method of diagnosis, they offer, after all, merely one of the methods of determining what is wrong; and the results obtained through such study must still be correlated with the results obtained by other methods.
How does allergy develop? In the answer to this question one should note with Simon1 the differences between one type of sensitivity, to serum or to poison ivy, for example, which occurs to a greater or lesser extent in all persons exposed to the foreign substance, and the other type, which occurs only in a small number of those exposed.