Physiology of Pathogenic Microbes. 75 



The disease develops when the phagocytes do not 

 succeed in killing the introduced germs ; in the op- 

 posite case it fails to develop. 



The injection of virulent germs in a susceptible in- 

 dividual paralyzes the phagocytes ; on the contrary, 

 the injection of attenuated germs is followed by an 

 accumulation of leucocytes (diapedesis) around the 

 place where the germs occur; the germs are then 

 taken into the substance of the leucocytes and di- 

 gested by them. The same thing happens when we 

 inject virulent germs into a non-susceptible subject. 



All the germs seized by the phagocytes are not in- 

 fallibly destroyed; hence, these migratory cells, in 

 certain cases, seem to be a means of transferring 

 bacteria from one part of the organism to another. 



The leucocytes possess, in common with some of 

 the lower vegetables, the property (called chemotaxis) 

 of moving themselves toward certain chemical sub- 

 stances. Now, experiments have shown that the 

 sterilized or filtered cultures of a certain number of 

 mjcrobes attract the white corpuscles, whilst cultures 

 of other microbes either have no action upon white 

 corpuscles or paralyze their movements. 



Some germs secrete substances which paralyze the 

 vaso-dilator nerves, thus opposing a direct obstacle to 

 diapedesis and therefore to phagocytosis. As an il- 

 lustration of this nervous action we find that the ear 

 of the rabbit which has received an injection of the 

 soluble products of the pyocyanic bacillus, for ex- 

 ample, does not become inflamed when a layer of 

 croton oil is applied to it. 



