200 Chapter VII 



A recent investigation, carried out by Bordet^ in collaboration 

 with Gengou, devoted to the study of the absorption of cytases 

 by micro-organisms that have been sensibilised by means of fixa- 

 tives, also gives us information on the question which now occupies 

 [211] us. It was easy to demonstrate the presence of fixative in the 

 serums in the case of the cholera vibrio and its allies, by reason 

 of their transformation into granules, appreciable on microscopical 

 examination. When a serum, which of itself is incapable of set- 

 ting up this transformation, produces it directly we add another 

 serum heated to 55° C, we must conclude that the latter fluid 

 contains the cholera fixative, whilst the former contains only cytases. 

 But, as the majority of bacteria do not undergo any analogous trans- 

 formation in serums, we are, in these cases, without any criterion as 

 to the presence of fixative. Bordet and Gengou have eliminated this 

 inconvenience in determining the fixation of alexine by bacteria 

 which undergo neither granular transformation nor any other visible 

 change. A normal unheated serum, which always contains a sufficient 

 quantity of cytases, is mixed with any micro-organism, e.g. with the 

 anthrax bacillus or the cocco-bacillus of plague. The serum, decanted 

 after a prolonged contact with these bacteria, remains quite as capable 

 of dissolving the red corpuscles of a determined foreign species as it 

 was originally. This proves that cytases remain in the serum and 

 that they have not been absorbed by the bacteria. Repeat the same 

 experiment with this difference, that instead of normal anthrax bacilli 

 or plague cocco-bacilli we introduce into the unheated normal serum 

 these bacteria after they have been sensibilised by the corresponding 

 fixatives (that is to say, previously submitted to the influence of specific 

 serums heated to 55° C). After contact for a certain length of time 

 with these bacteria the serum is no longer capable of dissolving the 

 red corpuscles of a determined foreign species, thus demonstrating 

 that the cytases have, thanks to the help of the fixatives, been linked 

 to the bacteria. We see, therefore, that it is easy to determine 

 whether a serum, whose properties are unknown, contains fixatives 

 or not. It is heated to 55° C. and mixed with normal unheated serum 

 to which bacteria are added. If, after contact with these latter 

 the normal serum has lost the power of dissolving the red corpuscles 

 (which it was capable of dissolving previously), it is because its 

 cytases, thanks to the fixative which must be present in the heated 



1 Aiui. de I'Inst. Pasteur^ Paris, 1901, t. xv, p. 289. 



