528 BOYNTON. 



One of the striking lesions in these septa is the enormous dis- 

 tention of the blood vessels, as shown in Plate I (e and /). In 

 some instances, these vessels contain large numbers of leuco- 

 cytes situated around the periphery; in others, they are scat- 

 tered uniformly throughout the blood stream, indicating that 

 there has been a slowing or even complete stasis of the flow. 

 This is undoubtedly caused by thrombus formation, as both 

 parietal and obturating thrombi are present, Plate I (b and e). 

 The presence of a parietal thrombus partly occluding the ves- 

 sel is shown in Plate I (e). This particular thrombus is of the 

 gray type, being composed of fibrin and leucocytes, while the rest 

 of the vessel is filled with blood. The vessel wall is undergoing 

 degeneration. A few mixed and two organizing thrombi have 

 been noticed, but as a rule they are of the gray variety. 



The accumulations of leucocytes around the blood vessels in 

 the septa are not so marked as those seen in the epimysium and 

 subcutaneous tissue. 



Extending from the septa are connective-tissue bands des- 

 ignated as the perimysium which divide the muscle into primary 

 bundles or fasciculi. This perimysium is also distended with a 

 fibrinous exudate intermixed with leucocytes. In places in the 

 perimysium thus affected, the vessels are distended with blood, 

 both parietal and obturating thrombi being present. Plate 1(6) 

 shows an obturating thrombus becoming organized. In many 

 instances the vessel walls are undergoing degeneration, emigrat- 

 ing leucocytes are seen passing through them, and also diapedesis 

 of red cells occurring. 



The perimysium is not all affected alike. For instance, in 

 Plate I (h) it is not so distended, contains a few leucocytes, 

 some fibrin, and also new-forming connective-tissue cells, thus 

 taking on more of the chronic type of inflammation. This may 

 be accounted for by the fact that the pleuropneumonia virus 

 seems to attack primarily the connective tissue, and as the process 

 extends downward into the areas where there is less connective 

 tissue there would naturally be fewer changes as there is less 

 material for the virus to work upon. Where the virus is not 

 sufliciently abundant to bring about marked changes, its con- 

 tinuous irritating action may be the cause of the chronic inflam- 

 matory process. In those areas where new-forming connective 

 tissue is present, new-forming blood vessels are occasionally seen, 

 slightly congested, but no thrombus formations have been noticed 

 in these particular parts. 



