66 ESSENTIALS OP BACTERIOLOGY. 



Cellular Theory of Metschinkoff, The phagocytes, as he 

 terms them, are auti-microbie. They are the soldiers which 

 endeavor to destroy the enemy. If the cells are strong, they 

 become the victors ; if the bacteria are stronger, the bacteria 

 conquer and eat up the cells. 



But this theory, though having many supporters, is opposed 

 on sufficient grounds, the one reason being that whenever cells 

 become the residence of live bacteria they suffer ; and if Mets- 

 chinkoff and others have seen bacteria directly enter cells and 

 disappear, it is that they were destroyed before, and that the 



leucocytes only acted as scav- 

 FlG ' 38 ' engers. (Fig. 38.) 



And the late researches 

 with the serum of the blood 

 freed of its cellular elements, 

 and being directly anti-bac- 

 teric, would seem to place the 

 phagocytes in the background. 

 The matter is, however, by 

 no means settled. 



Phagocytes of Metschinkoff: a. Bacillus m , , , 



entering ; 6. Bacillus inclosed. T Sum U P. We have P" th - 



genic microbes such as give 



rise to products injurious to the animal organism. The infec- 

 tious ones can overcome the natural resistance of the animal 

 body and develop therein. The bacteria can have this activity 

 lessened or destroyed by agents which are injurious to their 

 products, so as to render them inactive. 



CHAPTER XIV. 



IMMUNITY. 



THE natural or acquired power of resistance to bacterial 

 influences is called immunity. 



Natural. As we have mentioned before, certain animals are 

 naturally not acted upon by bacteria that affect other animals. 

 We say the animal or person is immune by nature. 



