Immunity against micro-organisms 317 



Infusorian which cannot have even its motility affected by the direct 

 action of the fluid elements. In all these cases, of course, the im- 

 munity conferred by the serums is due to the final destruction of 

 the micro-organisms which invariably resolves itself into the same 

 fundamental act— digestion by the cytases, a phenomenon which can 

 only be produced at all quickly by the action of cytases contained 

 in the protective serums or that have escaped from the phagocytes 

 during phagolysis. The digestion by the cytases may also, and this 

 is usually the case, be effected only after the manifestation of a regular 

 series of vital phenomena on the part of the defensive elements 

 of the body. As this factor fills such an important role, it is readily 

 understood that we can not accept the term passive immunity by 

 which to designate the immunity conferred by the specific serums. 

 The action of the cytases, which is necessary to bring about the final [333] 

 result in this immunity, depends too much on the activity of the 

 cells which contain the bactericidal ferment. For this reason, when 

 the functional activity of the phagocytes is in abeyance or is retarded, 

 the animal succumbs, in spite of the presence in its organism of a 

 more than sufficient quantity of cytases. In this connection Wasser- 

 mann's^ suggestion of adding normal serums rich in cytases to the 

 specific serums must be regarded as very apposite. When protective 

 serums poor in cytases or which have lost them as the result of 

 heating, of the use of antiseptics, or simply from the influence of 

 time, are injected, no immunising effect is ever obtained, simply be- 

 cause of the inactivity of the phagocytes, the cells in which the cytases 

 are found. If at the same time normal serum rich in cytases ready 

 prepared be injected, better results should be obtained. We may 

 recall here an analogous example — the anthrax of the rat. Although 

 possessing a large quantity of cytase, very effective against the bacillus, 

 the organism of the rat can make no use of it, because the phagocytes 

 which contain it do not manifest a sufficient activity. But the 

 injection into a rat of blood serum from the same species containing 

 a certain amount of cytase that has escaped during the formation of 

 the clot, is sufficient to preserve the animal against a fatal infection. 



To support his view, sound in principle, Wassermann made an 

 experiment the interpretation of which presents certain difficulties. 

 He injected guinea-pigs with protective antityphoid serum, in a dose 

 insufficient to protect them against a fatal infection. By introducing 

 along with this serum a certain quantity of normal ox serum which, 

 1 Deutsche med. Wchnschr., Leipzig, 1900, S. 285. 



