XIX. 



THE HEART AND BLOOD-VESSELS. 



229 



lowest. With a camel's-hair pencil dipped in normal saline solution 

 brush away all the brain matter, leaving a somewhat villous-looking 

 surface. Cut out a small part of the membrane, and mount it in 

 normal saline. 



(a. ) Find a capillary, note its diameter, uniform calibre, and oval 

 nuclei bulging slightly into the lumen of the tube. 

 The rest of the wall is homogeneous (fig. 214). 

 Trace it backwards until the small artery or arteriole 

 with which it is continuous is found. 



(b.) A small artery or arteriole with a thin 

 outer coat, and a middle coat composed of a single 

 layer of smooth muscular fibres arranged circularly FIG. 214. Capii- 



,, laries of Brain, 



(fig, 2l6;. fresh, x JOG. 



(c.) Select a small vein which is somewhat 

 thinner than the corresponding artery ; the muscular coat is very 

 i m perfect. Irrigate with 2 per cent, acetic acido Nuclei wherever 

 present come distinctly into view. 



(</.) The oval nuclei of the lining endothelium, the long axis of 



FIG. 215. A A small artery with the 

 lumen in focus. B. Small arteriole 

 just before it passes into a capil- 

 lary, x 300. 



FlG. 216. Small Artery from 

 Human Brain, Pigment 

 Granules in the Adven- 

 titia, x 150. 



the nuclei in the long axis of the vessel. Outside this the elastic 

 lamina appears as a somewhat refractive membrane with longi- 

 tudinal folds. 



(e.) The vessel crossed transversely by the long, oval nuclei of 

 the muscular fibres of the middle coat (fig. 216). Note in some 

 cases they are not distributed at equal distances, but in groups 

 (fig. 215). One point must he particularly studied, viz., to focus 

 tli rough the thickness of a small vessel, and observe carefully that 

 the- appearance of the vessel varies with the position of the lens, 

 i.e., whether the upper surface, lumen, or deeper part of the artery 

 is in focus. 



