LYMPHATIC VESSELS. 



of the walls, although the walls themselves are very 

 thin in proportion to the size of the lumen. Fol- 

 lowing the larger lymphatics toward the periphery, 

 we find that they pass over into irregular-branching 

 and pouching channels, the walls of which consist 

 of a single layer of endothelial cells, whose edges 

 are very sinuous, dovetailing into one another like 

 the pieces of a child's puzzle-map. These channels 

 are called lymphatic capillaries. Between these and 

 certain spaces or lacunae in the tissues those, for 

 example, in which the connective-tissue cells lie (see 

 page 47) there seems to be a direct communica- 

 tion, by means of which fluids, and probably formed 

 elements, such as blood-cells, pass over from the 

 blood into the lymphatic vessels. 



TECHNIQUE. 



Capillaries. The general appearance of the capillaries, 

 as well as of the smaller arteries and veins, is best seen 

 in those parts in which the vessels are surrounded by 

 but little tissue, as in thin membranes such as the mes- 

 entery or pia mater. A slice about an inch thick should 

 be made from the surface of the cerebrum and laid for 

 twenty-four hours in Mtiller's fluid. A small fragment 

 from that part of the pia which dips into the sulci should 

 now be carefully separated from the brain substance, 

 stretched on a bit of thin cork, and fastened with pins. 

 It is then laid for twenty-four hours each, in dilute and 

 strong alcohol, and finally stained double and mounted 

 in glycerin ; or balsam. 



