Acquired immunity against micro-organisms 285 



the fact that they mixed the leucocytes with blood serum. They 

 appear to have lost sight of the fact that this fluid is far from 

 corresponding to that which bathes the leucocytes in the living 

 animal. The serums contain leucotoxin in greater or less quantity 

 and it is not to be wondered at that the leucocytes when mixed with 

 normal rabbit's serum should perish very rapidly. Further, the 

 serum of vaccinated rabbits is agglutinative (this fact, however, was 

 not sufficiently elucidated in 1894 when the researches of Denys and 

 Leclef were made) and the clumping of streptococci might simulate 

 their destruction. In a word, the experiments of these observers 

 have been carried out under such conditions that it is impossible to 

 base upon them a refutation of data obtained in the living animal. 

 Moreover, in the description of the phenomena which appear in the 

 subcutaneous tissue of rabbits inoculated with the streptococcus, 

 Denys and Leclef provide us with arguments against their own 

 view. 



These observers introduce the same quantity of streptococci 

 below the skin of the ear of normal and of vaccinated rabbits. In 

 the first there is soon produced a very marked oedema of the ear, in 

 which may be seen a number of streptococci and of leucocytes that 

 have not ingested any micro-organisms. In the second the oedema 

 does not develop, but at the seat of invasion a number of leucocytes 

 come up and these soon ingest the streptococci. As we see, the 

 phenomena manifest themselves here just as they do with the anthrax 

 bacillus and many other micro-organisms when under analogous 

 conditions. Denys and Leclef, indeed, recognise that, below the skin 

 of the ear of vaccinated rabbits, the small quantity of exudation 

 fluid is not sufficient to enable us to accept it as capable of exerting 

 any considerable influence as regards humoral properties. Neverthe- 

 less, they think that the " serum " of this fluid may exercise a certain 

 action, but they furnish no proof of this, and seem to ignore the fact 

 that the plasma of the subcutaneous exudation is far from being 

 identical with blood serum obtained outside the animal. At present 

 it is well known that this latter fluid contains cytases which are[300j 

 absent from the plasmas. Now, the feeble bactericidal action, if this 

 really exists as regards the streptococcus, must be attributed to the 

 microcytase which has escaped from the leucocytes at the time of the 

 preparation of the serum. 



To sum up, the example studied by Denys and Leclef clearly 

 comes under the general law of phagocytic reaction in acquired 



