96 INFECTION AND RESISTANCE 



Since the phenomenon of antibody formation is not at all limited 

 to bacteria or bacterial derivatives, it cannot be looked upon merely as 

 a mechanism existing for the primary purpose of protecting the body 

 against infectious disease. This latter function is important, indeed, 

 but is probably incidental to the broader significance of the processes. 



In the course of normal existence substances which are not di- 

 rectly assimilable as such foreign proteins, for instance do not 

 penetrate directly into the blood and tissues. Taken into the ali- 

 mentary canal, they are first hydrolized into peptons, albumoses, 

 polypeptids, and probably amino-acids before absorption, to be recon- 

 structed from these cleavage products ("Bausteine" is Abderhalden's 

 expression for the amino-acids) into protein biologically identical 

 with that of the tissues. Digestive and other accidents, however, on 

 numerous occasions during life permit the direct entrance of these 

 materials unchanged or insufficiently changed into the circulation. 

 It is probably by the action of digestive powers of the serum or, in 

 the case of 'the entrance of undissolved foreign particles, by the 

 activity of the phagocytic cells that such substances are then dis- 

 posed ot and assimilated. For each particular variety of substance 

 (antigen) a specific mechanism is called into play, and when this 

 mechanism is repeatedly called upon as in successive injections of 

 foreign proteins this mechanism, whatever it may consist of, is en- 

 hanced in efficiency i. e., increased in quantity. How this increase 

 of specific antibodies is theoretically conceived we will discuss later 

 in connection with Ehrlich's side-chain theory. 



The phenomena of antibody formation against bacteria on this 

 basis may be taken to constitute, then, a mechanism for the digestion 

 and disposal of a foreign protein which has penetrated into the tis- 

 sues and, because of its living state, increases within the body by 

 multiplication, furnishing progressive stimulation to the antibody- 

 producing function. Infectious disease, therefore, from this point 

 of view may be looked upon as an invasion of the body by a living 

 foreign protein which must be assimilated and disposed of; which, 

 in some cases, has a primary toxicity per se ; and which is variously 

 distributed among the organs and tissues according to the biological 

 peculiarities of the particular microorganism in question. This 

 general conception will become more clear as we analyze the phe- 

 nomena associated with the individual antibodies. It is, of course, 

 quite plausible as far as it refers to the phagocytic functions, or even 

 bacteriolytic and cytolytic phenomena. It has been less clear in 

 connection with the agglutinins and precipitins in which a direct de- 

 fensive or bacteria-destroying value is not apparent. However, in 

 our discussions of these phenomena we will have occasion to point, out 

 many reasons for assuming that, even in these phenomena, there are 

 features which fall into direct correlation with the views we have 

 just expressed. 



