COMPOUNDS OF CARBON WITH OXYdKN AND MTKOdEN 369 



anhydride in this air may be detected by its action on lime water. 

 By allowing the seeds of plants to grow under a bell jar, or in a 

 closed vessel, the formation of carbonic anhydride may be similarly 

 confirmed. By forcing an animal, for instance a mouse, to remain 

 under a bell jar, the quantity of carbonic acid which it evolves may 

 be exactly determined, and it will be found to be many grams per day 

 for a mouse. Such experiments on the respiration of animals have 

 been also made with great exactitude with large animals, such as 

 men, bulls, sheep, &c. By means of enormous hermetically-closed bell 

 receivers and the analysis of the gases evolved during respiration it 

 was found that a man expels about 900 grams (more than two 

 pounds) of carbonic anhydride per diem, and absorbs during this time 

 700 grams of oxygen. 1 It must be remarked that the carbonic anhy- 



1 The quantity of carbonic acid gas exhaled by a man during the twenty-four hours 

 is not evenly distributed ; during the night more oxygen is taken in than during the 

 day (by night, in twelve hours, about 450 grams), and more carbonic anhydride is sepa- 

 rated by day than during night-time and repose ; thus, of the 900 grams separated 

 during the twenty-four hours about 375 are given out during the night and 525 by day. 

 This depends on the separation of carbonic anhydride during any kind of work per- 

 formed by the man. During the day-time his activity in many respects is comparatively 

 greater than by night. Every movement is the result of some change of matter, because 

 force cannot be produced by itself (in accordance with the law of the conservation of 

 energy). Proportionally to the amount of carbon consumed an amount of force is stored 

 up in the organism ami is consumed in the various movements performed by animals. 

 This is proved by the fact that during work-time, in twelve hours, a man exhales 900 

 grams of carbonic anhydride instead of 525, absorbing the same amount of oxygen as 

 before. In a working day a man exhales by night almost the same amount of carbonic 

 an hydride as in a day of rest, so that during a total twenty-four hours' work a man 

 exhales about 1300 grams of carbonic anhydride and absorbs about 950 grams of 

 cxygen. Therefore in work the change of matter increases. The carbon expended on the 

 work is obtained from the food ; on this account the food of animals ought certainly to 

 contain carbonaceous substances capable of dissolving under the action of the digestive 

 fluids, and of passing into the blood, or, in other words, capable of being digested. Such 

 food for man and all other animals is formed of vegetable matter, or of parts of other 

 animals. The latter in every case obtain their carbonaceous matter from plants, in 

 which it is formed by the separation of the carbon from the carbonic anhydride taken up 

 during the day by the respiration of the plants. The green parts of plants during the 

 day absorb the carbonic anhydride of the air, and find it ample notwithstanding the 

 small proportion of it in the air, and give out oxygen. The volume of the oxygen exhaled 

 is almost equal to the volume of the carbonic anhydride absorbed ; that is to say, nearly 

 all the oxygen entering into the plant in the form of carbonic anhydride is separated in 

 a free state, whilst the carbon from the carbonic anhydride remains in the plant. At 

 the same time, the plant absorbs moisture by its leaves and roots. By a process which 

 is unknown to us, this absorbed moisture and carbon remaining from the carbonic acid 

 enter into the composition of the plants in the form of so-called carbohydrates, com- 

 posing the greater part of the vegetable tissues, starch and cellulose of the composition 

 C(jH lo O 5 being representatives of them. We may represent their composition as a com- 

 pound of carbon remaining from carbonic acid and water, 6C + 5H.,,O. In this way a 

 circulation of the carbon goes on in nature by means of vegetable and animal organisms,, 

 in which changes the principal item is the carbonic anhydride of the air. 



VOL. I. B B 



