THEORIES OF IMMUNITY 153 



This theory explains the specificity of the antitoxins for a given 

 toxin; thus the latter causes specific chemical stimulation of the cell, 

 which induces the formation of specific side-chains, the cast-off re- 

 ceptors, which are capable of uniting with the toxin molecules free in 

 the body-fluids and thus neutralizing them; they are, therefore, called 

 antitoxins. 



This theory also explains why a minute quantity of toxin is capable 

 of stimulating the production of a large amount of antitoxin, and why 

 the production of antitoxin persists for some time. The toxin molecule 

 must be conceived as entering into the protoplasm of a body molecule 

 and residing there for some time, acting as a stimulus to the cell, with 

 consequent production of antitoxin. Diagrammatic 

 representations of this process would seem to show 

 that a physical union exists between toxin and cell 

 receptors, resulting in the destruction of receptor, 

 which drops off and is replaced by a number of recep- 

 tors that, for lack of space for attachment to the 



cell, are thrown off into the blood-stream. In FlG - 40. THEO- 



RETIC STRUC- 

 reality, by the act of immunization certain cells of TURE OF A MOLE- 



the body become converted into cells that secrete E X 



specific antitoxin, and, as shown by Salmonson and 1, Toxin: H, 

 Madsen, the administration of pilocarpin, which 



augments the secretion of most glands, also pro- receptors of cells or 

 . , . , . , . ... antitoxin; T, toxo- 



duces in immunized animals a rapid increase in the phore group. 



antitoxin content of the serum. The formation of , 2 > Toxoid: Same 



structure as toxin 

 antitoxin is constantly going on, and so throughout molecule except 



a long period the antitoxin content of the serum gr o up is \o P 

 remains nearly constant. 



In the production of antitoxin the haptophore group is the essential 

 and important portion of the toxin molecule. Even though the toxo- 

 phore group is lost, and when this occurs the toxin is called toxoid 

 (Fig. 40), the haptophore group is capable of uniting with receptors 

 and stimulates the production of antitoxin. In fact, in effecting immu- 

 nization with powerful toxins it may be necessary, in the first few in- 

 jections that are given, to convert artificially all or a portion of the 

 toxin into toxoid, so that antitoxins will be produced that will protect 

 the animal against subsequent overdoses of toxin. 



The production of antitoxins must, in keeping with this theory, be 

 regarded as a function of the haptophore group of the toxin. It is easy, 

 therefore, to understand why, out of the great number of alkaloids, 



