SPLANCHNOLOGY. 183 



contained in it. 275 parts by weight of carbonic acid contain 75 parts of 

 carbon and 200 of oxygen. In one hour 10.572 grammes of oxygen are 

 consumed, that is. 38.764 grammes of carbonic acid are generated. This 

 amount varies greatly, however, with age, sex, and external conditions. 



In mules the carbonic acid exhaled regularly increases from eight to thirty 

 years of age ; from thirty to forty it is stationary ; and from fifty to extreme 

 age it goes on diminishing. It is greater in males than in females at all 

 ages beyond eight years. In females, nearly the same proportionate increase 

 goes on to the time of puberty, wlien the quantity abruptly ceases to 

 increase, and remains stationary as long as menstruation continues, again to 

 increase when this ceases. , The more robust the individual, the greater is 

 the amount of carbonic acid given off. 



Although the volume of the nitrogen taken into the lungs remains nearly 

 the same, yet there is a constant absorption and exhalation of this gas. 

 The amount is somewhat greater in summer than in winter. There is 

 usually some organic matter contained- in exhaled air, either chemically or 

 mechanically, as sulphuric acid is reddened by being breathed through for 

 a considerable time. 



The reaction which takes place between the air and the blood is one of 

 simple endosmose and exosmose. If the blood come to the lungs charged 

 with carbonic acid, and is exposed in their cells to the influence of atmo- 

 spheric air, which is a mixture of oxygen and nitrogen, the carbonic acid 

 will pass out, to be replaced by oxygen and nitrogen. The quantity of 

 oxygen which enters will be much greater than that of nitrogen, owing to 

 the superior facility with which oxygen passes through porous membranes. 

 If the venous blood contain nitrogen as well as carbonic acid, it also will 

 pass out, to be replaced by oxygen. The relative amount of these several 

 interchanges of gases will be subject to continued variation from secondary 

 causes. The combination of oxygen with carbon, to form carbonic acid, 

 takes place not only in the lungs, but throughout the whole system, and this 

 combustion is attended with the evolution of a considerable amount of heat. 

 To this is mainly to be ascribed the animal heat of the body, which in man 

 amounts at a mean to about 100° F. 



VII. ORGANS OF DIGESTION. 



(SPLANCHNOLOGY.) 



The daily wear and tear of life, involving the destruction of life in indi- 

 vidual atoms of the body, the loss of matter in the secretions and excretions, 

 and the necessity of supplying fuel to keep up the temperature of the body, 

 all require the constant introduction of fresh organic matter to supply the 

 waste. A wise Providence has imparted to us certain sensations, known as 

 hunger and thirst, by means of which we are enabled to ascertain when 

 solid and liquid food is required. The various alimentary substances are 

 taken into the mouth and masticated by the teeth, then carried to the 



889 



