PRINCIPLES OF VETERINARY SURGERY 161 



aseptic fluids, chemicals, croton oil, turpentine, cells from 

 other animals, such as blood corpuscles and spermatozoa; 

 and in fact, most all foreign substances, when introduced 

 into an animal possess chemotactic power, both positive and 

 negative. 



The phagocytes choose bodies best suited for their use. 

 The macrophages seize by preference animal cells such as 

 blood corpuscles, spermatozoa and the animal parasites, 

 etc., and those micro-organisms which set up chronic dis- 

 eases like glanders, tuberculosis, actinomycosis, etc. The 

 macrophages can also ingest bacteria of acute diseases, but 

 with the exception of a few cases, their intervention is of 

 little moment. The microphages appear to play their part 

 especially in acute infection, such as one caused by strep- 

 tococci, hog cholera bacilli, etc. Their intervention against 

 animal cells is nil, or almost so. They appear to be repelled 

 by parasites of animal origin and by certain bacteria which 

 set up chronic processes. 



The morphological and physiological differences be- 

 tween the two great categories of mobile phagocytes cor- 

 respond to the differences in their soluble' ferments or 

 cytases. These cytases, (alexins of Buchner, or comple- 

 ments of Ehrlich) can be extracted from the leucocytes, 

 and under certain conditions are found free in the blood. 

 The macrocytase is capable of dissolving the red blood- 

 corpuscles and other cells, which the -microcytase will de- 

 stroy and digest many micro-organisms. Thus Metchnikofif 

 states that there are two kinds of cytase, while Ehrlich 

 holds that there are many kinds. These cytases are not 

 thrown off by the phagocytes so long as they remain intact. 

 When these cells are injured, however, they allow a part of 

 thejr cytase to escape, which gives to the blood its anti- 

 toxic, hemolytjc, and bactericidal properties. The destruc- 

 tion of the phagocytes by which the cytase is set free into 



