MINUTE ANATOMY OF THE CAPILLARIES. 



287 



the brain, spinal cord, and retina of man. The action of nitrate 

 of silver frequently brings into view irregular flat cells in their 

 substance, which are often fused into one another. By careful 

 treatment they may be obtained in the isolated condition. 



Fig. 53. A rather large capillary from the hyaloid of the Frog, pre- 

 senting a mtmbranous and nucleated tunica adventitia. 



This layer may be distinguished as the external vascular 

 epithelium, or still better as the vascular perithelium. 



The number of cells seen on a transverse section of a capil- 

 lary tube is, with few exceptions, dependent less on their size 

 than on their form, because the size of the cells in the capil- 

 laries corresponds with the calibre of the vessels. In the 



