126 ELEMENTARY PHYSIOLOGY. [XII. 



silver nitrate solution, or exposed too long to 

 light, silver will be deposited in the 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. 



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 Ip.c. to distinguish more clearly the elastic 

 from the white fibrous tissue. (The perforations 

 in the fenestrated membrane are rendered more 

 distinct by staining.) 



Tear off 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. 



