252 Chapter IX 



animals. It must be admitted that this ferment is not inseparably 

 bound to the cells which produce it, as is the case with the cytases. 

 I have already developed, at some length, the thesis that the cytases 

 remain, in the normal animal, within the phagocytes, and only escape 

 from them when these cells are destroyed, whether in the living 

 animal (during phagolysis) or outside the animal (during the prepa- 

 ration of the serum). Gengou's experiments with the plasma and 

 the blood serum of normal animals have completely confirmed the 

 fundamental observations that the cytases are not found free in the 

 circulating blood. It is evident that the same law applies also to 

 an animal that has acquired immunity. For this reason neither 

 Pfeiffer's phenomenon nor any analogous process that demands the 

 action of cytases is ever produced in the anterior chamber of the 

 eye, or in the subcutaneous tissue, or in oedema either active or 

 passive. Further, it is in virtue of this same law that Pfeiffer's 

 phenomenon does not manifest itself even in the peritoneal cavity or 

 in the blood vessels of vaccinated animals in which the phagocytes 

 have been protected from phagolysis by previous injections of 

 various fluids (physiological saline solution, broth, etc.). It would 

 be very interesting to be able to demonstrate the absence of cytases 

 in the fluids of immunised animals by experiments of the same order 

 as those carried out by Gengou with the fluids of normal animals, 

 but the obstacles to the realisation of this postulate are too great. 

 We saw when discussing Gengou's experiments that it is impossible 

 to obtain in vitro a fluid identical with the plasma of living blood. 

 The greatest precautions in collecting the blood and in its after 

 treatment are insufficient to prevent coagulation taking place sooner 

 or later. It follows that, as there is always a considerable quantity 

 of free fixative in the plasma of immunised animals, an infinitesimal 

 quantity of microcytase, set free from the leucocytes, is sufficient 

 for the production of Pfeiffer's or any other analogous phenomenon. 

 There must be a great improvement in the methods of preparation 

 of plasmas outside the body before it will be possible to undertake 

 successful researches on the above problem. For the present we 

 must rest satisfied with other proofs, already numerous and very 

 demonstrative, of the absence of free cytases in the normal plasmas of 

 vaccinated animals. 



[266] The cytases being found in about the same quantity and pre- 

 senting the same properties in all animals that enjoy immunity 

 whether natural or acquired, it must be the fixative which specially 



