[114] See Jacoby, *Immunität und Disposition*, Wiesbaden, 1906. [115] *Collected Studies on Immunity by Ehrlich and his Collaborators*, translated by Ch. Bolduan, New York and London, 1906. This phenomenon in particular--the production of *more* of the antitoxin or the “precipitin” than is actually necessary--seems to render almost impossible any merely chemical theory of these facts. The reaction between toxin and antitoxin, albumen and precipitin is indeed chemical; it may in fact be carried out in a test-tube; but whether the production of the anti-body itself is also chemical or not could hardly be ascertained without a careful and unbiassed analysis. There can be no doubt that the well-known theory of Ehrlich,[116] the so-called theory of side-chains (“Seitenkettentheorie”) has given a great impulse to the progress of science; but even this theory, irrespective of its admissibility in general, is not a real chemical one: the concept of a regeneration of its so-called haptophore groups is a strictly biological concept.[117] [116] So-called genuine or innate immunity, in contrast to the immunity which is acquired, is of course a case of adaptedness only and not of adaptation. There also exists a high degree of specific adaptedness in some animals with regard to their faculty of coagulating blood. (See Leo Loeb, *Biol. Bull.* 9, 1905.) [117] We cannot do more than barely mention here the problem of the localisation of anti-body production. In general it seems to be true that anti-bodies are produced by those cells which require to be protected against toxins; that would agree with the general rule, that all compensation of the change of any functional state proceeds from the part changed in its function. And, indeed, here if anywhere we have the biological phenomenon of adaptation in its clearest form. There are very abnormal changes of the functional state of the organism, and the organism is able to compensate these changes in their minutest detail in almost any case. The problem of the specification of the reactions leading to immunity seems to me, as far as I can judge as an outsider, to stand at present in the very forefront of the science. There cannot be the slightest doubt that especially against all sorts of foreign albumens the reaction is as strictly specific as possible; but there are some typical cases of specificity in the production of antitoxins also. It is, of course, the *fact* of specific correspondence between stimulus and reaction, that gives to immunity its central position among all adaptations, no matter whether the old hypothesis of the production of specific anti-bodies proves tenable, or whether, as has been urged more recently by some authors, the anti-body is always the same but reacts differently according to the medium. In the latter case it would be the medium that is regulated in some way by the organism in order to attain a specific adaptedness. NO GENERAL POSITIVE RESULT FROM THIS CHAPTER