I 



Mechanism of immunity against micro-organi^is 179 



of which we have cited above, leave no doubt that the ingestion of 

 micro-organisms unprovided with amoeboid powers takes place by 

 means of active movements of the living protoplasm of the leucocytes. 

 To dissipate any remaining doubt on the part of the reader I need 

 only recall Bordet's investigations, cited in the preceding chapter, of the 

 behaviour of leucocytes in the peritoneal cavity of guinea-pigs inocu- 

 lated with streptococci and Proteus bacilli. The leucocytes of the 

 peritoneal cavity allow the virulent streptococci to develop freely, not 

 ingesting a single one, whilst the Proteus bacilli, injected later, are 

 quickly devoured and at the end of a very short time are all found 

 in the substance of these same phagocytes. This example, so demon- 

 strative, of the chemiotaxis (positive as regards Bacillus proteus and 

 negative as regards the streptococcus), is at the same time the best 

 proof of the fact that the ingestion of the micro-organisms is a vital, 

 physiological act and not merely a simple phenomenon of mechanical 

 penetration of micro-organisms into the soft protoplasm of the 

 leucocytes. 



It was formerly thought that leucocytes, charged with micro- 

 organisms, provide the latter with a good culture medium and serve 

 also as vehicles of transport for them from one place to another in 

 the living organism. This view has often been affirmed without any 

 proof whatever being given of it. It has now been demonstrated 

 to be erroneous. The micro-organisms, with some rare exceptions, 

 find within the leucocytes a very unfavourable medium. Usually 

 they perish there, or, in the case of very resistant micro-organisms, 

 such as the tubercle bacilli in refractory animals or the endospores of 

 certain bacteria, without being actually destroyed, they are prevented 

 from germinating and multiplying. 



Later, another view has been advanced that phagocytes are 

 capable of ingesting only those micro-organisms that have been 

 previously killed by some substance which is found outside the 

 defensive cells. This view is quite as erroneous as the one we have 

 just analysed. The phagocytes are perfectly capable of seizing and 

 devouring living micro-organisms. We have only to recall on this point 

 the facts cited in the preceding chapter on the subject of living [190] 

 bacteria ingested by the leucocytes of various animals, or the history 

 of the very active spirilla which retain their motility up to the moment 

 when they become completely enclosed by the protoplasmic processes 

 of the leucocytes of the guinea-pig. Observations in vitro have, as 

 already described in the same chapter, afforded a demonstration of the 



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