6 3 



LESSON XVI. 

 BLOOD VESSELS. 



(a) Capillaries. 



The thoracic aorta of a rat or guinea pig was injected vvitli a 

 \% solution of silver nitrate. After 20 to 30 minutes the mesentery 

 was removed, pinned out on flat corks, placed in 95% alcohol, in 

 which the tissue was exposed to direct sunlight. In a few minutes 

 the tissue turns a brownish color. It was then dehydrated, cleared 

 in oil of bergamot,-and cut into small pieces. Mount in baisntn. -.'*, c^^ 



Study under high power. Small capillaries and arter- 

 ioles, the endothelial cells of which are outlined by 

 brownish-black lines, will be seen. Sketch a number of 

 the capillaries under high power. 



(b) Small Arterioles. 



The mesentery of a cat was pinned out on a cork, hardened in 

 alcohol, stained in Delafield's hsematoxylin, dehydrated, and cleared 

 in oil of bergainot. Mount in balsam. 



Study under high power. Look for arterioles consist- 

 ing of an endothelial coat, and a media composed of a 

 single or double layer of non-striped muscle cells, about 

 which there is a thin layer of fibrous tissue. Search for 

 capillaries, in which the nuclei of the endothelial cells are 

 stained. Sketch an arteriole and capillary as seen under 

 high power. 



(c) Artery and Vein. 



The posterior tibial artery and vein (human) were hardened 

 in mercuric chloride or alcohol, stained in borax carmine or Dela- 

 field's hajMiatoxylin, embedded in paraffin, and cross-sectioned. 

 Fix to the slide and mount in balsam. 



Study first under low power. In the wall of the artery 

 three coats are seen, 



