3 2 TOXINS AND ANTITOXINS. 



Phagocytosis.- -We have seen that an organism 

 subjected to a toxic invasion tends to protect itself 

 by proper means of defense; and one of those is 

 the direct putting into activity of the living cellular 

 elements themselves, and in particular, the leuco- 

 cytes, or white corpuscles, found in more or less 

 number, according to pathological conditions, in 

 the blood and lymphatic fluids.* 



Metchnikoff has shown that the moment a 

 foreign element, particularly a microbe, enters the 

 organism, these leucocytes come flocking from 

 all parts of the body, collect around the bacte- 

 rial element, penetrate it, and begin to digest it. 

 These elements have received the name phagocytes. 

 The name chemotaxis has been given to the prop- 

 erty by virtue of which they approach (positive 

 chemotaxis) or move away from (negative chemo- 

 taxis) certain substances which affect them power- 

 fully. 



Experiments have shown that the leucocytes 

 are attracted by the products secreted by patho- 

 genic microbes, or saprophytes. Attracted by 

 the latter, the white corpuscles surround, envelop, 

 and finally digest them; and when it happens that 

 all the pathogenic microbes within an organism 



* It is necessary here to consult the work by LEVADITI: 

 Le Leucocyte et ses Granulations. Sc'entia, Naud, publisher, 

 Paris, 1903; also METCHNIKOFF: I/Irnmunit, Paris, 1902, 

 publisher, 



