184 MANUAL OF BACTERIOLOGY. 



philic leucocytes become much more numerous in the blood 

 than normally. There is every reason for believing that the 

 leucocytes and other body cells play an important part in 

 combating bacteria. However, the doctrine of phagocytosis, 

 as primarily stated, is insufficient to account for many facts. 

 Metchnikoff himself has modified his original views, to con- 

 form with more recent studies. 



Ehrlich's Side-Chain Theory of Immunity. 1 This the- 

 ory was first proposed to explain the resistance of the 

 body to soluble bacterial poisons, as those of diphtheria and 

 tetanus. In these cases what is known as antitoxic immunity 

 is produced. With the infections in which the poisons occur 

 in the bodies of the bacteria the protective mechanism is 

 different, giving rise to the term bacteriolytic immunity. 



Antitoxic Immunity. Ehrlich first endeavored to ex- 

 plain from a chemical standpoint the action of toxins on 

 cellular protoplasm and the formation of antitoxins. To 

 begin with, the molecules of the protoplasm are to be re- 

 garded as being endowed with chemical groups, present in 

 the form of lateral appendages to the molecule, called side- 

 chains. They can be illustrated by the analogies presented 

 by the graphically written formulae of some complex mole- 

 cules. It is necessary to conceive of molecules made of an 

 immense number of atoms, and bristling with projecting 

 side-chains. The function of the side-chains is to become 

 attached to other organic molecules with which thev have 

 affinities. In this manner they aid in absorbing the sub- 

 stances essential for the nutrition of the protoplasm of cells. 



1 The literature of this subject is very extensive. An exhaustive 

 review is that by L. Aschoff, " Ehrlich's Seitenkettentheorie," ZeitscJmft 

 f. aUgcmcinc Physiologic, 1902. 



The following are also of a general character: H. C. Ernst, " Modern 

 Theories of ^pcternl Immunity," 1903; Prudden, Medical Record, 

 February i 1. 1003; RilrlrV. Journal of Hygiene, Vol. II., 1902; Bergey, 

 American Medicine, October n, 1902. 



