Immunity against pathogenic micro-organisms 157 



fact that the lymph is rich in leucocytes, whilst in the fluid of the 

 oedema they are almost absent ? Pursuing this question, Sawtchenko 

 made a comparative study of the bactericidal power of the serum, 

 prepared outside the body, and of the blood plasma obtained by 

 means of an extract of the heads of leeches, and he concluded 

 from his researches that the bactericidal substance circulates in the 

 plasma of the living rat and that it is not derived from the micro- 

 phages, but must be looked upon rather as a secretion of the macro- 

 phages in the blood and of endothelial cells. This result was not 

 confirmed by Gengou 1 , who also took up the study of this important 

 question in my laboratory. Instead of preparing the plasma by 

 means of the addition of an extract of leeches he made use of 

 a method much more perfect and free from sources of error. He 

 introduced no foreign substance capable of affecting the results of his 

 experiments. Collecting the rat's blood in paraffined tubes, and 

 centrifugalising it in similar tubes, he obtained a fluid which ap- 

 proaches much more closely the plasma of circulating blood than does 

 serum. This fluid, however, will coagulate at the end of a fairly long 

 interval, which proves that it cannot be looked upon as blood plasma. 

 Gengou examined the bactericidal power of the fluid portion of the 

 "plasma," obtained by the process just described, on the anthrax [i 67] 

 bacillus, and also that of serum prepared in tubes in the ordinary 

 way. The difference between the two fluids is very marked ; whilst 

 the serum destroys the bacilli sown in it very rapidly and dissolves 

 their contents, the fluid of the "plasma" has no similar action. 

 These results, confirmed several times, demonstrate very definitely 

 that the plasma of the circulating blood does not contain any bac- 

 tericidal substance. This, during the life of the animal, is found 

 inside leucocytes and only escapes from them when the cells burst 

 or undergo profound lesions, this taking place when the clot is 

 formed and when the serum is prepared outside the organism, or in 

 the eflused and coagulated blood, or again in the peritoneal lymph 

 during phagolysis. This phagolysis is inevitably produced as a result 

 of rapid injection of foreign fluids into the peritoneal cavity, e.g. 

 of broth or of physiological salt solution, containing bacteria in 

 suspension. 



The facts we have brought together on the subject of anthrax in 

 rats form a whole whose several parts are in complete harmony. The 

 phagocytes of this species of rodent contain a bactericidal ferment^ 



1 Ann. de I'lnst. Pasteur, Paris, 1901, t. xv, p. 232. 



