XIII] MICROBES OF MALIGNANT ANTHRAX 315 



smaller and in a few days has almost entirely disappeared. 

 By reinjection after the lapse of a week to a fortnight the 

 dose of culture or toxin can be made a little larger or the 

 virus a little more potent without again producing more 

 than the former transitory result. In this way Behring 1 

 was the first to show that the resistance of the animal can 

 be gradually more and more increased, inasmuch as after 

 repeated injections it is capable of resisting (except for the 

 transitory tumour and rise of temperature) larger and larger 

 and more potent doses of the virus, doses which at a former 

 stage would have at once produced fatal results. Behring 

 has thus succeeded in "immunising" sheep and goats to a 

 very high degree, that is to say that after many injections 

 with increasing amounts and potency the animals are 

 capable of resisting a dose of virus many times the former 

 fatal dose. Roux ^ uses for this purpose the horse, and he 

 succeeds after many injections (over thirty, extending over 

 nearly three months) in enabling this animal to at last 

 resist the intravenous injection of the prodigious amount 

 of 250 cc. of the most potent toxin. 



As is well established, diphtheria is a highly contagious 

 disease, transmissible from person to person, its contagium 

 belonging to the group called fixed contagia. But it is 

 likewise well established that milk infected from a human 

 source has, in several epidemics, been the means of pro- 

 ducing diphtheria in the consumers (Ballard). It is further 

 known that a room in which a diphtheria case has once 

 existed may for years harbour the contagium of diphtheria, 

 so that any new-comer or inhabitant may contract the 

 disease ; moreover, it is known that in a locality in which 

 diphtheria has once been rife the disease may at any time 

 reappear, and in these instances the transmission of the 



' Behring, Deutsche Med. Wochenschrift, 1890, No. 50. 

 '^ Roux, Annales de rinstittit Pasteur, September, 1894. 



