364 BACTERIOLOGY. 



hundred times as much antitoxin as is required for ten 

 fatal doses, the resistance of the animal it-elf account- 

 ing for the difference. 



5. The fact that the potency of antitoxin is greatly 

 increased if it is allowed to come in contact with the 

 toxin outside the animal body; and is increased still 

 further if allowed to remain for sufficient time in con- 

 tact with the toxin at a suitable temperature. 



On the other hand, the conclusions which Buchner 

 and Roux drew from their experiments have been shown 

 to have been based on a misconception, for they ignored 

 the capacity of an animal to deal with a certain minimal 

 quantity of poison, and, consequently, made no distinc- 

 tion between a physiologically neutral and a completely 

 neutral mixture. 



The facts now known, therefore, indicate rather 

 strongly that the antitoxins of tetanus and diphtheria, 

 of snake-poison, of ricin, etc., enter into direct chem- 

 ical combination with their respective toxins a com- 

 bination which is, perhaps, not exactly comparable to 

 that of an acid with an alkali; for, as we have seen, 

 it is a much slower one, but one which possibly as 

 Ehrlich has suggested more closely resembles the for- 

 mation of a double salt. Some facts seem to indicate 

 that the antitoxin has a stronger affinity for toxin than 

 the toxin has for the cells. Many points, however, are 

 still far from clear as to the manner in which both 

 toxins and antitoxins act. 



The Testing of Antitoxin. This power, possessed 

 by a definite quantity of antitoxin to neutralize a cer- 

 tain amount of toxin, is utilized in testing antitoxin. 

 Guinea-pigs of about 250 grammes' weight are sulicu- 

 taneously injected with one hundred or with ten fatal 



