BL OOD- VESSELS. 5 1 



MIDDLE-SIZED ARTERY. 



PREPARATION. Place a moderate-sized artery say the femoral or posterior tibial of 

 a child, or the basilar artery of a sheep or man in chromic acid and spirit for a week, and 

 make transverse sections. Stain one section with logwood, and mount it in dammar ; cover ; 

 another with picrocarmine, and mount in Farrant's solution. 



EXAMINATION (L). Observe the inner coat, perhaps with the layer of squames lining it. 

 Observe the elastic lamina, as a clear, yellow, bright line thrown into folds by the contraction 

 of the middle coat which surrounds it. If a large artery be under examination, a sub-epithelial 

 layer of delicate connective tissue may be found between the epithelium and the elastic 

 lamina. The elastic lamina is an important guide in disease of the blood-vessels, for if 

 changes take place internal to it, it is a disease of the inner coat ; if immediately external to it, 

 the disease is in the middle coat. The student should, therefore, familiarise himself with its 

 appearance, on account of its important pathological relations. The middle coat consists 

 chiefly of several layers of circularly disposed non-striped muscular fibres. The nuclei are 

 long ovals and of a violet colour. Between the fibres may be found elastic tissue. Outside 

 this note the adventitia, consisting mainly of white fibrous tissue stained blue, and containing 

 elastic fibres, especially in its inner part. (Indicate the epithelium, elastic lamina, and other 

 coats in PL IX., Fig. 8.) 



(H). Study the elastic lamina ; it is a good landmark in a section. On its inner surface 

 a profile view may be obtained of the lining epithelium. Observe the middle and outer coats. 



The Epithelium and its Cement-substance in blood-vessels is demonstrated by the use of nitrate 

 of silver. For a class this is easily managed, thus : 



PREPARATION. Kill an etherised rabbit by bleeding. Open the thorax and place a 

 cannula in the aorta, and (after making an opening in the inferior cava), wash out the blood- 

 vessels with distilled water. Then inject the vessels with a half per cent, solution of silver nitrate. 

 Cut out the intestines and wash out their contents, and then expose them and their mesentery 

 in a mixture of equal parts of spirit and water to sunlight till they become brown. Select either 

 a piece of the mesentery which contains blood-vessels, or what answers equally well, take a piece 

 of the small or large intestine and lay it on a slide with its mucous surface upwards. With a 

 scalpel scrape away the mucous coat and mount the muscular and serous coats in dammar. 



EXAMINATION (L. and H). Select a small artery, notice the silver lines running trans- 

 versely, indicating the disposition of the circular muscular fibres, and inside these black 

 silver lines mapping out narrow lanceolate areas with their long axis in the. axis of the vessel 

 which are the squames lining the artery. Try and find a vein and compare the epithelium of 

 the two vessels. Trace an artery until it splits up into capillaries, and study the silver lines in 

 a capillary. These indicate that it is made up of elongated flattened endothelial cells. If it 

 be desired to reveal the nuclei in these plates, a section should be stained with logwood. 

 (Indicate the silver lines in a capillary in PI. IX., Fig. 4, and in the artery in Fig. 5.) 



VEINS. 



Exactly the same methods are employed for bringing into view their structure. Many 

 sections of them will be found in other organs. They are recognised by their thin walls, the 

 absence of so perfectly defined an elastic lamina, their thinner muscular coat, and the less 

 distinct demarcation of their individual coats. 



