SUSCEPTIBILITY AND IMMUNITY. 229 



to the highly alkaline reaction of the blood and tissue juices of this 

 animal. Behring claims to have obtained experimental proof of the 

 truth of this explanation by feeding white rats on an exclusively 

 vegetable diet or by adding acid phosphate of lime to their food, by 

 which means this excessive alkalinity of the blood is diminished. 

 Rats so treated are said to lose their natural immunity, and to die as 

 a result of inoculation with virulent cultures of the anthrax bacillus. 



The recent experiments of Nuttall, Behring, Buchner, and others 

 have established the fact that recently drawn blood of various ani- 

 mals possesses decided germicidal power, and Buchner has shown 

 that this property belongs to the fluid part of the blood and not to 

 its cellular elements. It has also been shown that aqueous humor, 

 the fluid of ascites, and lymph from the dorsal lymph sac of a frog 

 possess the same power. This power to kill bacteria is destroyed by 

 heat, and is lost when the blood has been kept for a considerable 

 time, but it is not neutralized by freezing. Further, this power to 

 destroy bacteria differs greatly for different species, being very de- 

 cided in the case of certain pathogenic bacteria, less so for others, 

 and absent in the case of certain common saprophytes. Behring 

 has also shown that the blood of different animals differs consider- 

 ably in this regard, and that the blood of the rat and of the frog, 

 which animals have a natural immunity against anthrax, is espe- 

 cially fatal to the anthrax bacillus. The experiments made show 

 that this germicidal power is very prompt in its action, but that it is 

 limited as to the number of bacteria which can be destroyed by a 

 given quantity of blood serum. When the number is excessive, de- 

 velopment occurs after an interval during which a limited destruc- 

 tion has taken place. It would appear that the element in the blood 

 to which this germicidal action is due is neutralized in exercising 

 this power ; and as, independently of this, blood serum is an excel- 

 lent culture medium for bacteria, an abundant development takes 

 place when the destruction has been incomplete. 



Buchner has ascribed this remarkable property of blood serum to 

 the presence of some albuminoid substance, the exact nature of 

 which he was not able to determine ; and quite recently Hankin 

 (1891) has published the results of his interesting researches con- 

 firming this view. From the spleen and blood serum of rats he has 

 isolated a globulin possessing germicidal properties, to which he 

 ascribes the power of rat's blood to destroy anthrax bacilli, without, 

 however, rejecting the view that the excessive alkalinity of the 

 blood of this animal may be a factor in producing this result. The 

 globulin obtained by him is insoluble in water or in alcohol and does 

 not dialyze. 



In a recent communication (1892) Brieger, Kitasato, and Wasser. 



