722 MICROBIOLOGY OF DISEASES OF MAN AND DOMESTIC ANIMALS 



that the body tissues did not possess the necessary food products for 

 the invading microorganisms and that in acquired immunity these 

 necessary food products were exhausted completely so that when a sec- 

 ond infection was attempted none could possibly occur. This theory 

 has also been discarded. 



One of the most prominent theories is the one which has been 

 held more recently, with some modifications, namely, the chemical 

 side-chain theory of Ehrlich. It is claimed that tissue cells are made 

 up of definite chemical substances which possess chemical side-chains 

 which are open for chemical combination with other substances. 

 It is by means of these chemical side-chains that food products are 

 absorbed and assimilated by the cells. Furthermore, it is by means 

 of these chemical side-chains that toxins and various poisons are 

 absorbed by the cells. It seems to have been clearly demonstrated 

 that as a result of the absorption by certain cells of the body of toxic 

 substances, particularly bacterial toxins, that the cells are stimulated 

 and produce or open up a excenss of these chemical side-chains for 

 combination with various substances. It is conceived that if enough 

 toxin (not enough to kill the cells), is assimilated by the cells the 

 chemical side-chains which are definite chemical substances will be 

 split off from the original cell compound and escape into the circulation. 

 It is these escaped chemical side-chains which constitute the antitoxin 

 or bactericidal substances. In the case of antitoxins, they possess 

 a maximum affinity for the toxin and will combine with the toxin much 

 more readily than the toxin will combine with the remaining chemical 

 side-chains of the original cell compound. In the case of bacteri- 

 cidal substances they will combine with the bacteria and destroy them 

 and liberate in this way the endotoxins which may subsequently combine 

 with an tiendo toxin (?) or tissue cells. Inasmuch as no antiendo- 

 toxins are ever produced, the presence of bactericidal substances in 

 a large percent of instances is a detrimental factor. The production 

 of antiendotoxins by some method or other is extremely desirable. 

 Since the majority of our diseases are due to bacteria producing endo- 

 toxins, such a product would be of immense value in combating these 

 infections. The chemical theory of Ehrlich explains many features 

 of the phenomena of immunity. This theory has been the basis of 

 nearly all of the preceding discussions on the various antibodies. 



