Mechanism of immunity against micro-organisms 201 



serum, have been absorbed by the bacteria. In the other case, we 

 conclude the non-existence of the fixative. 



In their researches, Bordet and Gengou often employed normal 

 unheated serums to which they added several species of bacteria. 

 They demonstrated that in these mixtures the cytases remained [212] 

 intact or nearly so. These soluble ferments were scarcely, if at 

 all, absorbed by the bacteria, which proves that in the normal 

 serums there are no fixatives in any appreciable quantity. Of all 

 their experiments the one that interests us most was carried out 

 with Proteus vulgaris. This organism placed in prolonged contact 

 with normal guinea-pig's serum showed itself incapable of absorbing 

 or fixing anything beyond the most minute quantities of the cytases. 

 There is consequently no fixative for Proteus in normal guinea-pig's 

 serum, or, if any exists, it is only in negligible quantity. And yet 

 this same Proteus vulgaris^ when injected into guinea-pigs, was in 

 a short time ingested and destroyed by the phagocytes which assure 

 to the animal a natural immunity of the most stable character. The 

 facility Avith which the leucocytes of the guinea-pig devour the 

 Proteus follows, among others, from an experiment by Bordet^ 

 carried out with quite another object. A guinea-pig, very ill as the 

 result of the injection into its peritoneal cavity of a very virulent 

 streptococcus, contained in the peritoneal exudation a quantity of 

 empty microphages incapable of ingesting these streptococci. At 

 this critical moment there was injected into the same position a 

 mass of Proteus vulgaris. " At the end of a very short time, it is 

 seen that the leucocytes which energetically refuse to ingest strepto- 

 cocci greedily seize upon the new organism ofiered to them ; and at 

 the end of half-an-hour the whole of these organisms are found in- 

 side phagocytes." 



Here, then, we have an actual proof of the fact that the phago- 

 cytes, in order to rid the animal organism of a microbe and assure 

 to it a natural immunity, have no need of any previous help from an 

 extraphagocytic fixative. The phagocytes act, so to speak, motu 

 proprio, and themselves bring about the resorption of the intruders. 

 The question of fixatives in normal serums, then, loses its importance 

 for us and their origin no longer presents any essential interest for 

 the problem with which we are at present occupied. 



Can we conclude, from the data just summarised, that the cytases, 



1 Ann. de VInst. Pasteur, Paris, 1896, t. x, p. 107. 



