IMMUNITY?. 



i8s 



dose of diphtheria or tetanus toxin may be neutralized out- 

 side of the body by mixing it with its appropriate antitoxin. 

 Injection of the mixture shows it to be innocuous to animals. 



The manner in which toxins combine with protoplasm has 

 been shown in the case of tetanus toxin. The filtrate from 

 cultures of tetanus bacilh will kill guinea-pigs, presumably 

 by damage to the cen- 

 tral nervous system. 

 The same filtrate 

 rubbed up with brain 

 or spinal cord has been 

 found to have lost its 

 toxic properties. It 

 may be assumed that 

 the poison has com- 

 bined with the proto- 

 plasm of the cells. 



But the side-chain 

 theory offers an ex- 

 planation not only of 

 the mechanism of the 

 union of toxin and 

 antitoxin, but also ex- 

 plains the phenomena 

 of agglutination, pre- 

 cipitation, and cytol- 

 ysis. In the union of 

 antitoxin and toxin, as 



stated above, the process is a simple combining of the toxm 

 with the receptor, and there the process ends. Receptors of 

 this kind are called receptors of the first order (Fig. 48). But 

 after the union of the agglutinins and of the precipitins with 

 their receptors further change takes place. In the one case, 

 clumping; in the other, precipitation; and these changes are 

 16 



Fig. 49. — Receptors of the Second Order 

 AND OF Some Substance Uniting with 

 One of Them. — {Journal of the Ameri- 

 can-Medical Association. 1905. P. 1113.) 



c. Cell receptor of the second order, d. Tox- 

 ophore or zymophore group of the recep- 

 tor, e. Haptophore of the receptor. /. 

 Food substance or product of bacterial 

 disintegration uniting with the haptophore 

 of the cell receptor. 



