526 BOYNTON. 



approximately from 50 to 160 microns in diameter. Located in 

 or near the center of these areas are either single or ramified 

 blood vessels distended with blood. In some instances these 

 contain a considerable number of leucocytes, which are as a rule 

 situated near the vessel wall, showing that the blood stream had 

 been retarded in its flow. It is a known fact that "a greater or 

 less number of leucocytes pass over into the peripheral plasma 

 zone, when the slowing of the circulation has reached a certain 

 degree." (2) 



In some instances the vessel walls apparently have not deviated 

 from normal to any great extent, while in others migration 

 of leucocytes and diapedesis of red cells may be observed. 



The dark-staining areas situated around the blood vessels 

 take on different appearances at different stages of develop- 

 ment, of which four can be easily recognized. 



First. The congested blood vessel is surrounded by a zone of 

 leucocytes, being composed of both round cells and polynuclears. 

 These areas average from 50 to 70 microns in diameter. 



Secondly. The congested blood vessels are surrounded by a zone 

 of round cells and polynuclear leucocytes. Around this is a 

 zone of broken down leucocytes and cell detritus intermixed with 

 the fibrinous exudate. These areas average from 80 to 120 

 microns in diameter. 



Thirdly. The congested blood vessels are surrounded by a light- 

 staining zone of new-forming connective-tissue cells, intermixed 

 with a few leucocytes, and in some instances new-forming blood 

 vessels which are congested. Around this zone of new-forming 

 connective tissue is a deeper staining zone composed of leucocytes, 

 and situated around this area is a zone of broken down leuco- 

 cytes and cell detritus extending into the fibrinous exudate. 

 These areas average from 100 to 160 microns in diameter. 

 (Plate IV.) Hence it will be noticed that as the irritant persists, 

 a chronic inflammation is produced, which leads to the production 

 of new-forming connective tissue and of blood vessels. 



Fourthly. In a few instances blood vessels are completely oc- 

 cluded by thrombus formations. In these cases the vessel walls 

 are degenerated to a considerable extent and leucocytes situated 

 around them are undergoing karyorrhexis. 



Where the blood vessels are situated close together, the in- 

 flammatory zones around them coalesce, forming oblong dark- 

 staining areas or bands, with the congested vessels in the center, 

 and the deeper staining areas of leucocytes along the periphery. 



Summarizing the changes which take place in the older lesions, 



