126 ELEMENTARY PHYSIOLOGY. [XII. 



silver nitrate solution, or exposed too long to 

 light, silver will be deposited in tlie substance 

 of the cells also. 



A vein is here taken as being a somewhat easier 

 preparation for a student than an artery ; the main 

 features in either case are the same. 



3. Cut open longitudinally a large artery, e.g. carotid 

 of sheep, from a freshly killed animal, and very 

 gently scrape the internal surface. Tease out 

 the material so obtained in normal saline solu- 

 tion. 



Observe in surface and profile the cells of the 

 lining epithelium, with their elongated nuclei. 

 Probably there will also be seen fragments of 

 the .elastic fenestrated membrane. Add acetic 

 acid 1 p.c. to distinguish more clearly the elastic 

 from the white fibrous tissue. (The perforations 

 in the fenestrated membrane are rendered more 

 distinct by staining.) 



4. Tear ofif a strip from the inner coat of a medium- 

 sized artery which has been in potassium bichro- 

 mate "2 p. c. for two to six days ; tease it out in 

 the fluid ; it will be found to consist almost en- 

 tirely of elastic laminae. 



Observe the gradations from an almost homo- 

 geneous elastic perforated membrane to a mesh- 

 work of elastic fibres. 



