2l8 MANUAL OF BACTERIOLOGY. 



It has already been explained that the neutralization of 

 bacterial poisons or toxins takes place by the production of 

 antitoxins (page 209), and that the gradual injection of toxins 

 is followed by a greatly increased production of antitoxin. 

 Bacteriolysins, then, may be produced — or at least their pro- 

 duction may be stimulated — by injections of bacteria, while 

 antitoxins are produced by injections of toxins; and Ehrlich 

 advanced his now celebrated side-chain theory to explain these 

 phenomena as well as the formation of agglutinins, lysins and 

 precipitins. 



Ehrlich's Side-chain Theory of Immunity.* — Ehrlich 

 was the first to offer an explanation from a cheipical point of 

 view of the action of toxins on cellular protoplasm and the for- 

 mation of antitoxins. He assumes, to begin with, that the 

 molecules of the protoplasm are to be regarded as being en- 

 dowed with chemical groups, present in the form of lateral ap- 

 pendages to the molecule, called side-chains. They can be 

 illustrated by the analogies presented by the graphically writ- 

 ten formulae of some complex molecules. 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 they have affinities. In this manner they aid in 

 absorbing the substances essential for the nutrition of the 

 protoplasm of cells. 



The side-chains are therefore also called "receptors" — a more 

 appropriate name. The numerous receptors which a molecule 



*The literature of this subject is very extensive. An exhaustive review is 

 that by L. Aschoff. Ehrlich's Seitenkettentheorie. Zeitschrift jiir allgemeine 

 Physiologie. igo2. 



The following are also of a general character: EhrUch's Croonian Lecture 

 Proceedings of the Royal Society. LXII., p. 437. igoo. Ehrlich. Schluss- 

 betractungen. Nothnagel's .System of Medicine. Vol. VIII. H. C. Ernst. 

 Modern Theories of Bacterial Immunity. 1903. Prudden. Medical Record 

 February 74, 1903. Ritchie. Journal oj Hygiene. Vol. II. 1902. Bergey 

 American Medichw. October 11, 1902. Immunity. Special Article. Journal 

 o] ihe American Medical Association. No. 4 et seq. 190^. ' 



