LYMPHATIC VESSELS. 129 



The arterioles may be prepared by pulling out some of 

 the arteries which enter the brain substance ; at the ends 

 of these the arterioles into which they divide are seen. 

 Some of the finer twigs are cut off, stained double, 

 mounted in balsam, and studied entire. 



In larger vessels this simple method is no longer prac- 

 ticable, and we have to resort to actual sections. Small 

 or medium-sized arteries and veins may be prepared by 

 stretching them, when fresh, along a bit of wood, with 

 pins, and hardening in alcohol. They are then imbed- 

 ded in celloidiri, sections made in any desired direction, 

 stained double and mounted in balsam. 



Large vessels, such as the aorta, vena cava, etc., may 

 be hardened in alcohol, imbedded in celloidin, and sec- 

 tions stained and mounted as above. 

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