DESCRIPTION OF TISSUES 197 



by these cells of red blood corpuscles and white blood cells. 

 Small clumps of proliferated endothelial cells occur as com- 

 pact, discrete lesions. Occasionally in the portal spaces they 

 are small, similar proliferative lesions composed of endothelial 

 cells. Blood vessel lesions are not found. Large necroses, 

 which are common in guinea-pig livers from many sources, 

 were naturally found in a number of our typhus guinea-pigs 

 and show no distinctive histology. 



(g) The gastro-intestinal tract: The gastro-intestinal tract 

 was studied microscopically from a few guinea-pigs. No 

 lesions of typhus were found. 



(h) The pancreas: No lesions of the parenchyma or blood 

 vessels were found. 



(i) The kidneys: The only lesions found in the kidneys are 

 small collections of cells about capillaries in the medulla. 

 These occur with great rarity in only a few kidneys. The cells 

 are large and evidently of endothelial origin. Mitoses occur 

 in such cell groups. 



(j) The adrenals: No lesions were found. 



(k) The skeletal muscles: No lesions were found. 



(1) The uterus and ovaries: No lesions were found. 



(m) The testes: The testes and adnexa are second only to 

 the brain in number and typical character of the lesions. 

 Vascular lesions, proliferative perivascular reactions and 

 simple perivascular infiltrations are found in the testes, epi- 

 didymis, tunica, cremasteric muscle, and polar fat. These 

 lesions are comparable to those found in man and in the skin 

 and subcutaneous tissues of the scrotum of the guinea-pig. 



Arteries and veins of considerable size, as well as capillaries, 

 are affected. Fibrin thromboses are rare, but occur. The 

 commonest lesion is a mural thrombus composed of prolifer- 

 ated endothelial cells and such accumulations may almost 

 occlude large vessels. A concentric thickening of the intima 

 by endothelial proliferation also occurs. The perivascular 

 proliferative reaction usually completely surrounds large and 

 small vessels, including capillaries, and the cell most abundant 

 is that which we have been calling endothelial leucocytes 



