Acquired immunity against micro-organisms 293 



outcome of this work was that " it was the bone-marrow, the spleen, 

 and the lymphatic system, including the thymus gland, which ex- 

 hibited immunising power against the bacillus of typhoid fever, whilst 

 the other organs, the blood, brain, spinal cord, muscles, liver, kidney, 

 etc., did not at this stage show any marked specific property." 



As these observations on the production of protective substance in 

 the phagocytic organs was one of essential importance in connection 

 with the problem of acquired immunity, I asked M. Deutsch 1 , working 

 in my laboratory, to carry out a series of experiments on this subject. 

 Using guinea -pigs, he injected into the peritoneal cavity cultures of 

 the typhoid bacillus killed by heat (66 C.). A few days later the 

 serum had become distinctly protective. At this stage, and even 

 before the appearance of this property in the blood, Deutsch killed 

 some of his animals and carefully measured the protective power of 

 the extract of the various organs. He began by confirming the result 

 obtained by Pfeiffer and Marx as to the non-production of the pro- 

 tective substance in the peritoneal exudation. Usually this fluid was 

 insufficient to protect normal guinea-pigs against typhoid infection. 

 In a few experiments only was the exudation found to be as pro- 

 tective as the blood serum ; in most of the others, the blood serum 

 was much more active than the fluid of the exudation. The spleen 

 was the organ which exhibited the greatest protective power, and [308] 

 in nearly one half of the cases it was more active than was the blood. 

 The bone-marrow sometimes gave analogous though much less marked 

 results. The spleen consequently must be looked upon as the principal 

 seat of the production of the protective substance. 



Having confirmed this observation of Pfeiffer and Marx and of 

 Wassermann and Takaki, Deutsch tried to obtain the protective 

 property in guinea-pigs deprived of their spleens. The experiment 

 was quite successful, and here again his result agreed with that 

 obtained by Pfeifter and Marx. Guinea-pigs from which the spleen 

 had been removed developed the protective property just as well as 

 did the control animals ; in the former the bone-marrow was found to 

 be specially active. 



When Deutsch, instead of removing the spleen from his guinea- 

 pigs before the injection of the micro-organisms, did so some (3 5) 

 days afterwards, there often occurred a marked diminution in the 

 amount of the protective substance produced. We must conclude, 

 therefore, that soon after inoculation there appeal's in the spleen 

 1 Ann. de Flnst. Pasteur, Paris, 1899, t. xin, p. 689. 



