366 DIPHTHERIA. 



The Toxins of Diphtheria. — As in the above experiments the 

 symptoms of poisoning and ultimately a fatal result occur when 

 the bacilli are diminishing in number, or even after they have 

 practically disappeared, Roux and Yersin inferred that the chief 

 effects were produced by toxins, and this supposition they 

 proved to be correct. They showed that broth cultures of three 

 or four weeks' growth freed from bacilli by filtration were highly 

 toxic. The filtrate when injected into guinea-pigs and other 

 animals produces practically the same effects as the living 

 bacilli ; locally there is less fibrinous exudation but a consider- 

 able amount of inflammatory oedema, and, if the animal survive 

 long enough, necrosis in varying degree of the superficial tissues 

 may follow. The toxicity may be so great that .05 c.c. or even 

 less may be fatal to a guinea-pig in twenty-four hours. 



After injection either of the toxin or of the living bacilli, 

 when the animals, such as guinea-pigs, rabbits, dogs, etc., survive 

 long enough, paralytic phenomena may occur. The hind limbs 

 are usually affected first, the paralysis afterwards extending to 

 other parts, though sometimes the fore limbs and neck first show 

 the condition. Sometimes symptoms of paralysis do not appear 

 till two or three weeks after inoculation. After paralysis has 

 appeared, a fatal result usually follows in the smaller animals, 

 but in dogs recovery may take place. There is evidence that 

 these paralytic phenomena are produced by toxoids, i.e. modified 

 toxins (p. 179), as they may occur when there is injected along 

 with the toxin sufficient antitoxin to neutralise the more rapidly 

 acting toxin proper. One point of much interest is the high 

 degree of resistance to the toxin possessed by mice and rats. 

 Roux and Yersin, for example, found that 2 c.c. of toxin, which 

 was sufficient to kill a rabbit in sixty hours, had no effect on a 

 mouse, whilst of this toxin even y^^- c.c. produced extensive 

 necrosis of the skin of the guinea-pig. 



Preparation of the Toxin. — The obtaining of a very active 

 toxin in large quantities is an essential in the preparation of 

 anti-diphtheritic serum. Certain conditions favour the develop- 

 ment of a high degree of toxicity, viz., a free supply of oxygen, 

 the presence of a large proportion of peptone or albumin in the 

 medium, and the absence of substances which produce an acid 

 reaction. In the earlier work a current of sterile air was made 

 to pass over the surface of the medium, as it was found that by 



