IMMUNITY. 23 



a result of this treatment were immune at a later date (after 

 several weeks), when inoculated with a virulent culture of the 

 anthrax bacillus. In the same year (1890) Behring and Kita- 

 sato discovered that the blood of an animal which has an 

 acquired immunity against tetanus or diphtheria, when added 

 to a virulent culture of one or the other of these bacilli, 

 neutralizes the pathogenic power of such cultures, as shown 

 by inoculation into susceptible animals ; and also that cultures 

 from which the bacilli have been removed by filtration, and 

 which kill susceptible animals in very small amounts, have 

 their toxic potency destroyed by adding to them the blood of 

 an immune animal, which is thus directly proved to contain an 

 antitoxin, — which comparative experiments show not to be 

 present in the blood of non-immune animals. In the experi- 

 ments of Behring and Kitasato referred to, it was found that 

 5 c.c. of serum from the blood of an immune rabbit, mixed with 

 I c.c. of a virulent filtrate of the tetanus bacillus, and allowed 

 to stand for twenty-four hours, completely neutralized its toxic 

 power, as shown by inoculations in mice : 0.2 c.c. of this 

 mixture injected into a mouse was without effect, while 

 0.000 1 c.c. of the filtrate, without such admixture, was infallibly 

 fatal to mice. The mice inoculated with this mixture remained 

 immune for forty or fifty days, after which they gradually lost 

 their immunity. The blood or serum from an immune rabbit, 

 when preserved in a dark, cool place, retained its power of 

 neutralizing the tetanus toxalbumin for about a week, after 

 which time it gradually lost this power. Behring and Kitasato 

 have also shown that the serum of a diphtheria-immune rabbit 

 destroys the potent toxalbumin in diphtheria cultures. It does 

 not, however, possess any germicidal power against the diph- 

 theria bacillus. 



In 1 89 1 G. and F. Klemperer published an important 

 memoir, in which they give an account of their researches 

 relating to the question of immunity, etc., in animals subject 

 to the form of septicaemia produced by the micrococcus of 

 croupous pneumonia. They were able to produce immunity in 

 susceptible animals by introducing into their bodies filtered 

 cultures of this micrococcus, and proved by experiment that 



