BODY-JUICES. 115 



that the cells gradually break up the germs, apparently a 

 process of digestion. In an immune, phagocytosis is usually 

 very active, whereas in a susceptible animal there is little or 

 no phagocytosis. 



The question has been raised whether these cells take up 

 living bacteria or whether they simply act as scavengers by 

 removing the dead germs. Metschnikoff successfully isolated 

 leucocytes containing anthrax spores and transplanted them 

 to bouillon. The spores were set free by the death of the 

 leucocyte and developed rapidly into mature and active organ- 

 isms. This observation has been confirmed by others. It 

 has also been noted that the leucocyte does not always destroy 

 the germ, but that this may destroy the leucocyte. The 

 phagocytes at times exhibit a selective tendency for certain 

 bacteria. 



The leucocytes are repelled or attracted by certain sub- 

 stances. This property is known as chemotaxis. Chemotaxis 

 is either positive or negative. If positive, the chemotactic 

 substance attracts large numbers of leucocytes, when phago- 

 cytosis is very marked. In negative chemotaxis the leuco- 

 cytes are repelled ; phagocytosis is then absent. In natural 

 immunity positive chemotaxis is very apparent. The leuco- 

 cytes probably kill the bacteria by digesting them or by lib- 

 erating some chemical substance which destroys the germ. 

 This chemical substance may be nucleiic acid or nuclease. 

 The phagocytic theory of immunity is no longer tenable in 

 view of the extensive researches made within the last few 

 years. Phagocytosis is now regarded as the result rather than 

 the cause of immunity. 



Body -juices: In 1872 Lewis and Cunningham noted that 

 bacteria injected into the body disappeared completely within 

 a few hours. 



Other investigators, notably Fodorand Nuttall, in 1887-88, 

 demonstrated that the blood exhibited decided germicidal 

 powers for some time after its withdrawal from the body. 



The same bacteriolytic action was observed in other of the 

 tissue-fluids, such as ascitic and hydrocele fluids, aqueous 

 humor, etc. 



The germicidal power of the blood is destroyed by heating 



