408 STENGEL — SPECIFIC PRECIPITINS. IDec. 5, 



Ehrlich's attractive theory of immunity, which he calls the Side 

 Chain Theory, explains the development of immunity and other 

 problems connected with this question far more satisfactorily than 

 any previous hypothesis. He has shown very clearly that the im- 

 munizing substances are products of cell activity under the stimulus 

 of the bacterial toxins, but he has also called attention to the fact 

 that the principle involved in this elaboration of immunizing sub- 

 stances does not differ greatly from that which obtains in the case 

 of the ordinary process of nutrition of cells. In other words, there 

 is a chemical union of the nutrient substance with the cell body in 

 the case of assimilation of food and a similar chemical union in the 

 case of bacterial toxins. The molecular radicals, which have a 

 special affinity for the nutrient body or for the toxin, are entirely 

 comparable to the replaceable atomic groups of organic compounds, 

 such as the benzol ring, and may be displaced from the central 

 nucleus. Being products of the vital activity of the cell, reproduc- 

 tion of such atomic groups is possible, and indeed, according to a 

 well-known principle of pathology, destruction of the atom groups 

 occasions a replacement in excess, attended with a separation from 

 the parent nucleus and extrusion from the cell of the atomic group. 

 When toxins unite with cells the combining radicals or *' groups" 

 of the latter are utilized or in a sense destroyed and the cell pro- 

 duces new groups in excess — some or all of which are extruded into 

 the circulation. These liberated groups constitute antitoxin in the 

 case of immunity, and I refer to them here not from any bearing 

 on the question of toxic immunity to our present discussion, but to 

 develop the point that the production of such bodies is a question 

 of chemical nature, and that it does not necessarily involve the 

 action of a living germ. This is proved on the one hand by the 

 production of antitoxic substances by the introduction into the or- 

 ganism of inorganic or organic compounds, and on the other hand 

 by the fact that similar substances are produced when food stuffs 

 and various other organic substances are injected. This is true in 

 particular of the substances concerned in precipitation, and Ehrlich 

 in his later writings has made a strong point of the similarity in the 

 phenomena of precipitation and of bacteriolysis in so far as the 

 origin and essence of the active agents in question are concerned. 



To come more immediately to the subject, it has been found that 

 injections of milk, albuminous liquids of other sorts and compound 

 mixtures like urine and blood serum, when introduced into the 



