314 INFECTION AND IMMUNITY. 



(water-flea), a small transparent crustacean. The 

 disease was caused by a blastomyces which forms 

 a long needle-shaped spore. After being swal- 

 lowed by the animal the spores penetrate the in- 

 testinal wall into the body cavity where they are 

 surrounded, englobed and digested by the white 

 blood corpuscles. If this occurred with sufficient 

 vigor all the spores were disposed of and the ani- 

 mal recovered. Sometimes,, however, the spores 

 germinated even after they had become intracellu- 

 lar, and when the parasitic cells reached maturity 

 they apparently had the power of killing the leu- 

 cocytes through the agency of a secretion peculiar 

 to themselves. In the event that the latter proc- 

 ess was sufficiently extensive the tissues were soon 

 overrun with parasites and death resulted from a 

 septicemic condition. The observations were made 

 in the living transparent animal. 

 Natural Although the example cited seemed convincing, 



Immunity. ., ., , .. v 



it was, of course, necessary that observations 

 should extend over many infectious processes be- 

 fore phagocytosis as the cause of natural immunity 

 could be accepted as a general fact. This has been 

 done on rather broad lines by Metchnikoff and his 

 pupils, and the results have served to convince 

 them that the phagocytes are responsible for nat- 

 ural immunity in all instances, and that the de- 

 gree of natural immunity in a given case depends 

 on the degree of phagocytosis which is manifested 

 against the organism. As stated previously, the 

 microphage, with its microcytase, is held responsi- 

 ble for antibacterial immunity in most instances, 

 although the macrophage is concerned in certain 

 chronic infections. 



