PHENOMENA FOLLOWING IMMUNIZATION 95 



cussions. The first of these is composed of the true bacterial toxins 

 the vegetable poisons ricin, abrin, krotin and robin, snake venom, 

 the enzymes, and other substances grouped with these on page 87. 

 These antigens have certain characteristics which render them com- 

 parable to ferments, and they induce in the animal body the forma- 

 tion of specific neutralizing antibodies (antitoxin, antivenin, anti- 

 enzyme) which inactivate their respective antigens when mixed 

 with them in proportionate quantities, either in the test tube or in 

 the animal body. This characteristic alone separates them sharply 

 from other antigens. The remaining antigenic materials do not in- 

 duce antitoxin-like neutralizing substances, but call forth specific 

 lytic, agglutinating, precipitating, or opsonic properties. 



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 of 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, 



