PHAGOCYTOSIS 45 



animals can be immunized by gradually increased doses, it is held 

 by him that the educated leucocytes neutralize the poison by their 

 secretions. 



In the case of anthrax infection, animals infected with virulent 

 cultures of this organism quickly succumb, without exhibiting any 

 leucocytosis (negative chemotaxis). 



If the animal has been previously immunized with attenuated 

 culture the injection of a virulent culture is followed by an enormous 

 outpouring of leucocytes at the site (positive chemotaxis), while if 

 the site of the inoculation in the non-immune animal is examined, 

 only a few leucocytes, and some clear serum will be found. 



Toxins, if injected, cause a negative chemotaxis. If tetanus 

 spores are injected into an animal, together with some toxin, the 

 animal rapidly succumbs to tetanus, without evincing any leuco- 

 cytosis. If the spores are washed free from toxin, and injected, 

 active leucocytosis occurs and the animal survives. 



A mixed infection of a highly virulent culture, and a non- virulent 

 one, often hastens the action of the virulent one. It is supposed 

 that the non- virulent bacteria engage the leucocytes, so that these 

 cells cannot cope with the virulent ones. 



Phagocytosis thus plays an important part in the protection role 

 in natural immunity, but no satisfactory theory has yet been offered 

 in explanation of the protective process in acquired immunity, at 

 least against toxins and other soulble and unorganized poisons. 



In order to meet the criticisms arising after Ehrlich's theories, 

 Metchnikoff added to his theory by stating that complement and 

 anti-body are enzymic bodies derived from phagocytes. 



The cellulo-humeral theory claims the attention of most bacteri- 

 ologists, as the probable explanation of the phenomena of 

 immunity. 



It is certain that cells, either sessile or mobile, and fluids, are im- 

 portant means of internal defense. In order that this theory may 

 be comprehended, certain well known properties of normal 'and 

 artificially immunized serum must be understood. 



