ABSORPTION 



211 



surfaces of these cavities, however, are covered with a layer of endothelial 

 cells with sinuous margins. At intervals between these cells are to be found 

 small free openings which have received the name of stomata. 



The Blood-capillaries. The blood-capillaries not only permit of a 

 transudation of the liquid nutritive material from the blood across their 

 delicate walls, but are also engaged, if not in the resorption of a portion of 

 this transudate, at least in the absorption of waste products resulting from 

 tissue metabolism. 



The Blood-vessels. The blood-vessels the venules that arise from 

 the capillary-vessels gradually converge and unite to form veins which by 

 their union ever increase in size until they terminate in the inferior and 

 superior vena cava, both of which at their terminations communicate with 

 the right side of the heart. The blood containing the waste products ab- 

 sorbed from the tissues, is con- 

 ducted by these veins to the 

 right side of the heart, thence 

 by the pulmonic artery into the 

 lungs, where the carbon dioxid 

 is eliminated; the blood carrying 

 the remainder of the waste prod- 

 ucts is then conducted by the 

 pulmonic veins to the left side 

 of the heart by which it is dis- 

 charged into the arteries and dis- 

 tributed in part to the kidneys, 

 liver, skin and intestine; by these 

 organs the remaining waste prod- 

 ucts are excreted from the 

 blood. 



The Lymph-capillaries. 

 The lymph-capillaries in which 

 the lymph-vessels proper take 

 their origin are arranged in the 

 form of plexuses of quite ir- 

 regular shape. In most situa- 



FIG. 84. ORIGIN OF LYMPH-VESSELS FROM THE 

 CENTRAL TENDON OF THE DIAPHRAGM STAINED 

 WITH NITRATE OF SILVER, s. The lymph-spaces 

 and lymph-canals, communicating, at x with the 

 lymphatics, o. Origin of the lymphatics by the 



confluence of several juice canals. B. Capillary 

 blood-vessels. (Landois and Stirling.) 



tions they are intimately inter- 

 woven with the blood-vessels, 

 from which they can be readily 



distinguished by their larger caliber and irregular expansions. The wall of 

 the lymph-capillary is formed by a single layer of endothelial cells with 

 characteristic sinuous outlines. These capillaries anastomose very freely 

 one with another and communicate, on the one hand, with the lymph-spaces 

 and on the other with the lymph-vessels proper. It was formerly believed 

 that the communication of the lymph- capillary with the tissue space was 

 a direct one, the lymph flowing from the latter into the former through an 

 open passage-way. Recent investigation would indicate that this histologic 

 arrangement does not exist but that on the contrary the lymph-capillaries 

 are closed vessels and that the tissue space and the interior of the lymph- 

 capillary are separated one from the other by a thin partition of endothelial 

 cells. As the shape, size, etc., of both lymph-spaces and capillaries are 



