44 ABSORPTION. 



55. The passage of the blood through the right cavities of the 

 heart, is effected in the same manner as in the left cavities. Be- 

 tween the right auricle and right ventricle there also exists a valve, 

 called the tncuxnt'd valve, which prevents the blood from return- 

 ing from the ventricle into the auricle, (p. 42.Jig.8. $ p.4&.JigAQ.) 

 and by the contractions of this ventricle the blood is forced to 

 circulate in the vessels of the lungs and to arrive at the left 

 auricle. 



56. It is the ventricles, as we have seen, which force the blood 

 into the arteries and cause it to circulate. 



57. The auricles are a sort of reservoirs, designed to contain 

 the blood arriving by the veins, and to pour it into the correspon- 

 ding ventricles. 



58. Such is the march of the blood, not only in man and all 

 the mammalia, but also in birds ; in the sequel we shall see that 

 in reptiles and fishes, the structure of the heart is less complicated, 

 and that the blood follows a somewhat different direction. 



OF ABSORPTION. 



59. The blood, in passing through the veins from their capil- 

 lary origin in the substance of the organs to their termination in 

 the right auricle of the heart, carries with it all the fluids which in 

 some way filter through the parietes of these vessels. Fluid sub- 

 stances which may be in contact with the surface of the body and 

 of the great hollow cavities in its interior, or which are deposited 

 in the depth of the organs, are, as it were, pumped up, more or 

 less rapidly, and carried into the torrent of the circulation. 



60. To the passage of substances, of whatever kind-, from the ex- 

 terior, into t lie interior of t/ie b!ood ves*e Is through their parietes, 

 or particular canals, and their mixture with the blood, is given the 

 name of ABSORPTION. 



61. Substances thus absorbed, generally, penetrate directly in- 

 to the veins ; but under some circumstances they are carried 

 thither by particular canals, called lymphatic vessels. In des- 

 cribing the act of digestion, we shall have occasion to refer again 

 to these vessels. 



55. Ho\v is the passage of the blood through the right side of the heart 

 effected ? What valve exists between the right auricle, and right ventricle? 

 How ijj thp blood forred to circulate through the lungs ? 



56. What forces the blood into the arteries ? 



57. What are the auricles ? 



58. Is the structure of the heart, and the circulation the same in all 

 animals ? 



59. Do substances different from the blood enter into the circulation ? 



60. What is absorption ? 



61. Is absorption effected by the veins only ? 



