IMMUNITY. 171 



Lastly, that leucocytes appear to have the power 

 of destroying bacteria in some cases, has been 

 demonstrated by the researches of Metschnikoff, 



If anthrax bacilli are inoculated in the frog, the 

 white blood-cells are observed to incorporate an,d 

 destroy them until they entirely disappear, and the 

 animal is not affected. But if the animal, after 

 inoculation, is kept at a high temperature, the 

 bacilli increase so rapidly that they gain the upper 

 handover the leucocytes, and the animal succumbs. 



In septicaemia of mice the white blood-cells are 

 attacked and disintegrated by the bacilli in a 

 similar way. It is difficult, however, to accept any 

 explanation of immunity from these observations, 

 to suppose, for example, that immunity depends 

 upon the micro-organisms being unable to cope 

 with the leucocytes in certain species. It is difficult 

 to conceive that the leucocytes in the blood and 

 tissues in the field mouse are differently constituted 

 from those in the house mouse, so that they form 

 an effectual barrier in the one case, though so 

 readily destroyed in the other. 



