36G INFECTION AND IMMUNITY. 



other. There is no third substance with which one 

 or the other may unite. In the body, however, the 

 conditions are more complex ; in this case two com- 

 binations are possible for the toxin, one with the 

 antitoxin which has been introduced and a second 

 with the tissue cells. As an instance of the great 

 rapidity with which toxin may unite with cells, 

 the work of Heymans with tetanus toxin may be 

 cited. "Heymans found that, if all the blood were 

 removed from an animal a few minutes after the 

 injection of a single fatal dose of tetanus toxin 

 and the blood of another animal substituted, still 

 the animal died of tetanus" (Eitchie) ; that is to 

 say, all the toxin had been bound by the cells in 

 that brief time. 

 of Other experiments show that quantities of toxin 



Toxin toy , ,-, i IT -11 



Tissues, and antitoxin which are neutral when mixed be- 

 fore injection are not entirely neutral if injected 

 separately and at different points of the body. In 

 this instance some of the toxin has had time to 

 unite with tissue cells before it could come in con- 

 tact with the antitoxin. 



Certain work by Donitz illustrates not only the 

 rapidity with which toxin may be bound by the 

 tissue, but also the method by which antitoxin ef- 

 fects a cure. In relation to tetanus he found that 

 if the toxin were injected first and the antitoxin 

 four minutes later, a quantity of antitoxin, which 

 was slightly in excess of the neutralizing dose, was 

 required to prevent the development of tetanic 

 symptoms; if he waited eight minutes, six times 

 as much antitoxin; after sixteen minutes, twelve 

 times as much; after one hour, twenty-four times 

 the simple neutralizing dose was required. A few 

 hours later no amount of antitoxin could save the 



