102 PRACTICAL HISTOLOGY. 



regular lines that often look like a network of elastic fibres. 

 The vessel under observation has a distinct double contour. 

 The sharp inner line is due to the elastic membrane, and 

 the long somewhat irregular lines seen here and there 

 running along the vessel, generally result from the foldings 

 of this membrane on account of the collapsed state of 

 the vessel. Possibly at the end of a vessel the elastic 

 membrane may be found isolated from the other tissues. 



162. Examine (H.) a preparation of the elastic mem- 

 brane isolated as follows : Remove the basilar or other 

 artery from the base of the brain, e.g., of a sheep. Take a 

 short piece of the vessel, lay it open, add a drop of acetic 

 acid, tease with needles, and mount in glycerine. 



163. Examine (H.) a preparation of blood-vessels of 

 pia mater stained with carmine. It brings out the nuclei 

 of the muscular fibres. 



164. Examine (H.) a T. S. blood-vessel of medium 

 size stained with carmine. The muscular fibres, the elastic 

 membrane, and the nuclei of the epithelial lining will be 

 seen. Such a section as this will be found in the prepara- 

 tion of spinal cord yet to be obtained ( 245), and also in 

 the V. S. tongue ( 185). 



Transverse sections of blood-vessels in their fresh con- 

 dition may be readily made with the freezing microtome. 



1 64A. Examine capillaries and larger vessels with epithe- 

 lium silvered according to the method described in 329. 

 Such a preparation is preserved in glycerine. 



Numerous preparations of blood-vessels for preservation 

 will be found in the sections of organs yet to be made. 



CIRCULATION OF THE BLOOD. 



165. The circulation may be studied in the tail of the 

 fish and tadpole ; in the web, mesentery, tongue, and lung 

 of the frog ; and amongst warm-blooded animals in the 

 wing of the bat and the omentum of the guinea-pig. The 

 last requires to be kept carefully warmed on a special hot 

 stage devised by Strieker and Sanderson (see Quarterly 

 Microscop. Journ. Oct. 1870). 



