5 2 HISTOL OG V OF NUTRIENT FL i *// AS. 



lacteals. Our plan of study permits only a brief account of 

 their microscopic structure. 



The arteries, veins, and larger lymphatics consist of a lining 

 of endothelial cells, flat, irregular in shape, joined edge to 

 edge by cement. Next to this lining we find a layer of elastic 

 tissue, then a layer of transverse involuntary muscle fibers, 

 and an external layer of connective tissue. The arteries are 

 more richly supplied with muscular fibers than the veins. 

 The capillary blood vessels and the lymphatics in general, 

 more irregular in caliber than capillaries, consist of a single 

 layer of elongated endothelial plates joined by cement. 



3. Lacteals. The blood vessels of the stomach and .intes- 

 tinal canal may absorb many soluble alimentary substances 

 which have passed the epithelial lining, and those of the body- 

 may absorb some interstitial fluids, but fatty matters, and many 

 albuminoids, or colloids, after mixing with the fluids of the 

 pancreas, liver, etc., are emulsified and conveyed by the epi- 

 thelial cells in the villi of the intestine to the lacteal glands. 

 This stimulates the growth and multiplication of bioplasts, 

 which are carried with the fluid pabulum through the thoracic 

 duct into the blood. 



4. Lymphatics. The lymphatics exercise a selective influ- 

 ence on residual material which may have escaped into the 

 tissues, or which, although partially degenerated, as in lactifi- 

 cation after fatty degeneration, may serve for reconstruction. 

 This material is a stimulating pabulum for the growth of leu- 

 cocytes in the lymphatic glands, as chyle is in the lacteal 

 glands, and the combined products enter into the circulation. 

 The lymphatics form rich plexuses in all tissues and organs 

 whatever, and the smaller are termed lymphatic capillaries. 

 Sometimes, as in the brain, the blood vessels are ensheathed by 

 lymphatics, called the perivascular sheaths. The rootlets of 

 the lymphatics begin in the connective tissue of different 

 organs by a communicating system of crevices, spaces, or 

 canals of various sizes and shapes, which are generally with- 

 out endothelium. The lymphatic vessels are also connected 

 with lymph sinuses or cavities in various organs, as well as 

 with the serous cavities of the bodv. Thus the subdural and 



