PRACTICAL HISTOLOGY. 



[XIX. 



(/.) In the outer coat the elongated fusiform nuclei of the con- 

 nective tissue cells are arranged longitudinally. 



For a permanent preparation, the pia mater after being removed 

 is hardened in 2 per cent, potassic bichromate and preserved in 

 alcohol. A thin piece is selected and stained with logwood or with 

 eosin-logwood, and mounted in balsam. 



10. T.S. Small Artery and Vein. Select a small artery and 

 vein, harden in M tiller's fluid, stain in bulk with haematein, and 

 cut in paraffin. 



(H) Observe the three coats in each, but they are much thinner 

 in the vein than the artery. In the former the intima is very thin 

 and the outer coat relatively thicker (fig. 2 1 7). 



FIG. 217. T.S. Small Artery and Vein. A. Artery ; V. Vein ; N. Nerve. 



11. Injection of Silver Nitrate into Blood- Vessels. (i.) From 

 the aorta inject the blood-vessels of a rabbit with .25 per cent, 

 silver nitrate. Before doing so wash out the blood-vessels with 

 normal saline to remove all the blood, and then with distilled 

 water. Slit up the intestine, wash out its contents, and expose it 

 to light in alcohol and water. Scrape away the mucous membrane, 

 leaving only the muscular coats. Dehydrate a small piece and 

 mount it in balsam. It is easy to find large and small vessels as 

 well as capillaries. 



(a.) (H) Select a small artery, and note in it the endothelial 

 lining (fig. 219, E) and the circular muscular fibres mapped out 

 from each other by silver lines (m). 



