PHAGOCYTOSIS 215 



leucocytes in pathological processes, however. The local heat 

 of au inflamed area is due chiefly to the accumulation of blood 

 in the part, and would not influence the leucocytes to migrate 

 from the still warmer blood into the tissues. By increasing 

 motility, however, the temperature of fever may favor migration 

 and phagocytosis, and local application of heat to inflamed areas 

 may induce local leucocytic accumulation. In burns the dura- 

 tion of the period of excessive temperature is usually too brief 

 to account for the attraction of leucocytes that results ; this 

 accumulation is undoubtedly due to the products of the result- 

 ing cell degenerations. 



The influence of light, mechanical stimulation, and gravity 

 upon leucocytes seems not to have been studied. The phagocy- 

 tosis of insoluble non-nutritive particles has been ascribed to 

 taetile stimulation, but the details of the operation of such stim- 

 uli are unknown, and the entire question of tactile stimulation 

 is unsettled. In experiments with elder pith it has been ob- 

 served that leucocytes penetrate to the center, even when the 

 pith contains only physiological salt solution. As Adler re- 

 marks, it is difficult to explain such migration as due to tactile 

 stimuli ; but, on the other hand, no other explanation has been 

 offered. 



PHAGOCYTOSIS 



The engulfing of bacteria, cells, tissue products, etc., by leu- 

 cocytes seems to be but an extension of the phenomenon of 

 chemotaxis. When the substance toward which the leucocyte 

 is drawn is small enough, the leucocyte simply continues its 

 motion until it has flowed entirely about the particle. Later 

 the particle becomes, as a rule, more or less altered within the 

 cell, unless it is a perfectly insoluble substance, such as a bit 

 of coal-dust. This action upon the engulfed object is un- 

 doubtedly due to the action of intracellular enzymes. 1 Protozoa 

 take their food into a specialized digesting vacuole which has 

 been shown by Le Dantec 2 (in Stentor, Paramcecium, and some 

 other varieties) to contain a strongly acid fluid. Miss Green- 

 wood 3 has also demonstrated acid in several forms of protozoa, 

 which is formed under stimulation of injected particles, whether 

 nutritious or not. Mouton 4 has been able to extract from the 

 bodies of protozoa (rhizopods) a feebly proteolytic enzyme. 



1 See Opie, Jour. Exp. Med., 1906 (8), 410. 



2 Ann. d. 1' Inst. Pasteur, 1890 (4), 776. 



3 Jour, of Physiol., 1894 (16), 441. 



4 C. K. Acad/des Sciences, 1901 (133), 244. 



