432 



GENERAL PHYSIOLOGY 



whole series of substances of non-bacterial origin. Thus, Buchner 

 found that broth made of wheat flour and that made of pea flour 

 possess especially strong chemotactic power. Finally, Sicherer 

 ('96) has recently shown that under proper conditions the leucocytes 

 of warm-blooded animals outside the body exhibit their chemo- 

 tactic properties toward very varied substances for a long time, as 

 clearly as in the living body itself. 



The chemotaxis of leucocytes plays an important role in the 

 development of many animals. This is made clear especially by 

 the beautiful investigations of Kowalevsky ('87) upon insects. 

 When the fly-larva changes into the complete fly a metamor- 

 phosis that takes place fairly rapidly the organs of the larval 

 body, such as the creeping muscles, become superfluous, and 



FIQ. 209. 



209. Leucocytes destroying the muscles in the metamorphosis of the larva of the fly. The- 

 granular masses are leucocytes, the striped masses bits of muscle. (After Kowalevsky.) 



begin to degenerate. The substances formed at the beginning of 

 this degeneration have a strong chemotactic action upon the 

 leucocytes: the latter wander into the degenerating organs in 

 great crowds, and as genuine phagocytes devour the disintegrating 

 masses, and thus accelerate their removal (Fig. 209). It is charac- 

 teristic that the phagocytes manifest their activity only in insects 

 in which the metamorphosis takes place very rapidly ; but that in 

 others, as in the moth, and in the degeneration of the tail of the 

 tadpole, they have no share. Nevertheless, Metschnikoff was able 

 to demonstrate analogous phenomena in the development of 

 star-fishes. 



Chemotaxis is wide-spread in the flagellate Bacteria, Infusoria, and 

 swarm-spores. In Bacteria the phenomenon was first discovered 

 by Engelmann ('81, 1 ; '94), and was at once employed practically 



