24 BIOLOGICAL LECTURES. 



this immunity had a duration of at least six months. They 

 also arrived at the conclusion that the immunity induced by 

 injecting filtered cultures into susceptible animals is due to the 

 production of an antitoxin in the body of the animal. 



Brieger, Kitasato, and Wassermann have reported (1892) 

 their success in conferring immunity upon guinea pigs against 

 the pathogenic action of the cholera spirillum. They found 

 that attenuated cultures suitable for use as "vaccines" could 

 be obtained by cultivating the spirillum in bouillon made from 

 the thymus gland of the calf, by which means they have also 

 obtained attenuated cultures of the bacillus of diphtheria, the 

 bacillus of typhoid fever, the bacillus of tetanus and the strep- 

 tococcus of erysipelas. Guinea pigs inoculated with a culture 

 in thymus bouillon, which had been subjected to a temperature 

 of 65 C. for fifteen minutes, were found after twenty-four 

 hours to be immune against virulent cultures in twice the 

 amount which would otherwise have been fatal. 



During the past two or three years numerous additional 

 experiments have been reported which confirm the results 

 already referred to, and show that immunity may be produced 

 in a similar manner against the toxic products of various other 

 pathogenic bacteria, the typhoid bacillus, the " colon " bacillus, 

 streptococcus pyogenes, staphylococcus pyogenes aureus and 

 albus, etc. 



The Italian investigators, Tizzoni and Centanni, in 1892, 

 published a preliminary communication in which they gave the 

 results of experiments which appear to show that in guinea 

 pigs treated with tuberculin, by Koch's method, a substance 

 is developed which neutralizes the pathogenic potency of 

 the tubercle bacillus. Professor Tizzoni and his associate, 

 Dr. Schwarz, have also (1892) obtained evidence that there is 

 an antitoxin of rabies. Blood-serum taken from a rabbit 

 having an artificial immunity against this disease was found to 

 neutralize in vitro the virulence of the spinal marrow of a rabid 

 animal after a contact of five hours. The blood-serum of dogs 

 having an acquired immunity against rabies was found to have 

 a similar action, but in much less degree. The substance 

 (antitoxin) present in the blood-serum of an immune rabbit 



