PHAGOCYTOSIS 



281 



higher animals. Inflammation may be incited by a large number of 

 agencies chemical irritants, mechanical injury, or even by the in- 

 troduction of inactive and isotonic substances such as broth or salt 

 solution. 20 21 Yet in these cases the response, though essentially 

 similar in principle to that following invasion by bacteria, lacks 

 certain features especially interesting in the present connection, and 

 it will be most profitable for our purpose to consider in detail the 

 result of infection with pathogenic micro-organisms. 



If an emulsion of pyogenic staphylococci is injected into an ani- 

 mal subcutaneously the site of injection will soon become reddened 

 and swollen and microscopic examination will show, within a few 

 hours, a swelling and engorgement of the blood vessels. 



The injected cocci will be found to lie partly scattered in the 

 tissue spaces, in part within polynuclear leukocytes and connective 

 tissue cells which have begun to ingest them. The tissue spaces 

 will be swollen and 

 stretched by the 

 exudation of blood 

 serum from the ves- 

 sels. This condi- 

 tion will begin in 

 from 4 to 6 hours 

 after injection and 

 increase during the 

 next 24 hours in ex- 

 tent and severity, 

 according to the 

 quantity and viru- 

 lence of the cocci 

 injected. The con- 

 ditions which pre- 

 cede the wandering 

 of the p o 1 y m o r- 

 phonuclear leuko- 

 cytes out of the ves- 

 sels have been care- 

 fully studied in such thin tissues as the mesentery of a frog after 

 injury by trauma or acid. Within the vessels of the affected area 

 there is at first an acceleration of the blood stream, then a dilatation 

 of the capillaries and a slowing of the current. Leukocytes may now 

 be observed moving more slowly than the main stream, and keeping 

 close to the periphery along the walls of the vessels. Here and there 

 they seem interrupted in their movements and adhere to the vascular 

 wall. A little later these cells appear to pass through the wall of the 



20 See Adami. "Inflammation," Macmillan, London, 1909. 



21 See Adami, loc. cit. 



DIAGRAMMATIC REPRESENTATION OF LEUKOCYTES WAN- 

 DERING THROUGH CAPILLARY WALLS. 

 Adapted from Ribbert, "Lehrbuch der Allgemeinen 

 Pathologic," p. 337. 



