ANATOMY, PHYSIOLOGY, &C. 253 



Among the wild animals, as old age increases, the 

 teeth fall out, and the means of obtaining food thus 

 failing, the body sinks to rest. Man is the only 

 animal that can counteract the fatal consequences of 

 the loss of teeth. 



The Blood. 



Haller estimates the blood at about one-fifth the 

 weight of the adult body, which, in a person of middle 

 size, may be reckoned about 28 pounds weight, three- 

 fourths in the veins, and one-fourth in the arteries. 

 Its temperature in the human subject is 98 Fahr. 



Blood distends the cavities of the heart and blood- 

 vessels, and prevents their collapsing ; it also stimu- 

 lates to contraction the cavities of the heart and ves- 

 sels, by means of which the circulation of the blood 

 is performed ; it generates within itself animal heat, 

 which it also propagates through the body ; it nou- 

 rishes the whole body, and is the source from which 

 every secretion is separated. 



In the higher classes of animals, the blood is of a 

 red colour, florid in the arteries, and dingy in the 

 veins. In the process of aeration, the blood parts 

 with a portion of its carbon, which combines with a 

 portion of the air inspired, and passes into the state 

 of carbonic acid. The quantity of oxygen consumed 

 by this process has been rated at 26, 38, and 36 

 cubic inches. 



Circulation of the Blood. 



Professor Blumenbach estimates that the heart ex- 

 pels two ounces of blood at each contraction, taking 

 the number of pulsations at 75 per minute. The 

 whole mass of blood he reckoned at 33 pounds. 



Proceeding on these data, we shall find that the 

 blood completes its circulation, the whole of it pass- 

 ing through the heart, in about 2j minutes, and that 



