DIPHTHERIA 165 



ficially-induced immunity is discussed on p. 112 et seq. ; 

 but as much interest is now being taken in this method of 

 treatment as appHed to diphtheria, we give in detail one 

 method of its preparation and employment. 



To obtain antitoxin serum, it is first necessary to prepare 

 a toxin of known strength. This, on injection into suit- 

 able animals, causes some substance which we term an 

 ' antitoxin,' of opposite properties, to be produced ; and 

 when the blood serum of an animal so immunised is used 

 for injection into patients suffering from diphtheria, we 

 introduce into their circulation the same kind of substances 

 that are present at convalescence, and neutralise the 

 poisonous products of the organism. 



We first prepare the diphtheria toxin by growing a pure 

 culture of the Klebs-Loffler in alkaline beef-broth at 37° C. 

 in flat-bottomed flasks supplied with a regulated current of 

 sterile air. The growth first causes the liquid to become 

 cloudy, and a sediment eventually develops at the bottom 

 of the flasks, the liquid becoming clear again. As the 

 alkalinity of the medium becomes neutralised by the acid 

 metabolic products, the growth slackens, and the operation 

 is usually complete at the end of three weeks. It is 

 then filtered through a Pasteur- Chamberland filter, and its 

 strength has next to be ascertained, which is done experi- 

 mentally by finding what volume is required to produce the 

 death of a guinea-pig weighing 500 grammes in twenty- 

 four hours. This should be effected by yV centimetre, and 

 if at or near this standard, the toxin is ready to begin 

 the process of immunising an animal. Horses are used 

 for this purpose, since they are able to yield quantities 

 of serum without injury to their health. A quantity 

 of 10 c.c. is injected into a horse which is (so far as can 

 be ascertained by careful examination) in perfect health, 

 the place chosen for inoculation being the apex of the 



