150 PRACTICAL HISTOLOGY. 



and firm. The sections are removed by the lifter 

 from the oil of cloves and gently placed upon a slide, 

 the excess of oil of cloves is allowed to drain off or 

 is soaked up with blotting paper, a drop of the 

 mounting varnish is placed on the cover-glass, and 

 this is then quickly inverted over the sections. The 

 preparation is now complete and permanent, and 

 ready for examination ; but as it will be some while 

 before the mounting varnish has become hard to any 

 distance under the cover-glass, care should be taken 

 not to let this become shifted in any way, since such 

 treatment would probably crumple or otherwise 

 spoil the sections. 



Preparation 4. The smaller arteries and 

 veins and the capillaries. The elongated epi- 

 thelioid cells which form the walls of the capillaries, 

 and which line the arteries and veins, are readily 

 shown in silvered preparations of any vascular 

 tissue. It is most convenient to choose a vascular 

 membrane for the purpose, because more readily dis- 

 played, and of vascular membranes the mesentery 

 of the frog or toad is perhaps as easy to prepare as 

 another. The following is the mode of proceeding: 

 The animal (a male) having been decapitated and 

 the spinal cord destroyed, the trunk is suspended 

 for a few minutes by the lower limbs in order to 

 allow the blood to drain from the body as completely 

 as possible. The frog is then placed on its back, 

 and the abdomen freely opened. A loop of intes- 

 tine is seized with forceps and gently raised by an 

 assistant, while with a soft camel-hair pencil, mois- 

 tened with distilled water, the operator carefully 

 brushes the mesentery on both surfaces, carrying the 

 brush in every case from the intestine, not tow r ards 

 it. This brushing subserves two purposes in the 

 first place, the epithelioid cells of the serous mem- 

 brane, which would obstruct the passage of the 

 silver solution to the bloodvessels, are removed ; and 



