IMMUNITY AND SUSCEPTIBILITY. 1 29 



served the appearance of paralysis just like that pro- 

 duced by diphtheria toxin in a child injected with diph- 

 theria antitoxin. 



B. Theory that the antitoxin is an enzyme produced in 

 the culture. — This view of the subject is presented to us 

 by Emmerich and Low, 1 whose interesting observations 

 upon cultures of Bacillus pyocyaneus showed that among 

 the metabolic products of bacteria there are certain bac- 

 teriolytic ferments or enzymes which check the further 

 development of the culture after it has attained a certain 

 age, and ultimately dissolve the contained dead bodies of 

 its bacteria. By precipitating and concentrating they 

 were able to separate a substance — pyocyonase — which 

 quickly destroyed pyocyaneus and other bacilli, and when 

 administered to animals exerted a protective power against 

 both infection and intoxication. According to the view 

 of these experimenters, antitoxin is nothing more than 

 an enzyme similar in nature to the pyocyonase, whifch is 

 introduced into the animal with the cultures used for 

 immunization, and which, not being eliminated, accumu- 

 lates in the blood, to which it subsequently confers the 

 bacteria- and toxin-destroying functions. 



This theory is elaborated from most interesting and 

 suggestive observations, but, unfortunately, will not stand 

 the test of experimental investigation. 



In the first place, it would only apply to immunization 

 by cultures of bacteria or filtered cultures of bacteria in 

 which the cellular activities had generated the enzyme. 

 Or, if we could persuade ourselves that the activity of the 

 vegetable cells had been such that in ricin, abrin, venom, 

 and eel's blood there might be some analogous enzymic 

 product — a very doubtful matter — it could never be so 

 modified as to explain the immunity which Besredka 

 produced with arsenic and the anti-arsenine which de- 

 veloped in the blood of his rabbits. 



Again, by reference to the calculations made above, it 

 must be clear that the antitoxin cannot be such an 



1 Zeitschrift fiir Hygiene, 1899. 

 9 



