ORGANIC PROCESSES OF PLANTS AND ANIMALS. 1017 



will be remembered that oxygen is converted into carbonic acid, 

 by the combustion of carbon, without any change of volume. 

 Such should be the result if the oxygen absorbed in respiration 

 is wholly consumed in oxidating carbon, as it must be when 

 the food is purely farinaceous ; such articles of diet as starch, 

 sugar and gum containing already sufficient oxygen to convert 

 their hydrogen into water, and requiring oxygen therefore to 

 burn their carbon only. 



According to some observations, upon which reliance may 

 be placed, the oxygen which disappears in the respiration of 

 man is always a little more than the volume of carbonic acid 

 produced, which would indicate that a part of the oxygen is 

 consumed in oxidating other principles besides carbon, such as 

 the sulphur and phosphorus which are discharged in an oxidated 

 state in the urine ; and to a greater extent probably, in oxidating 

 hydrogen, with formation of water. In the respiration of car- 

 nivorous animals, the proportion of oxygen which disappears, 

 without being replaced by carbonic acid, is considerable, ac- 

 cording to the observations of Dulong, a fact which may be 

 connected with the decided excess of hydrogen over oxygen, in the 

 composition of their food. Carbonic acid is also exhaled from 

 the skin of man and other animals, as well as from the lungs. 

 The question of the absorption of nitrogen from the air, in the 

 respiration of animals, has been finally settled in the negative : 

 they are incapable of assimilating that element in a free state. 

 (Boussingault : Ann. de Chim. &c., Ixxi, 113, and 128). 

 It is certain, however that nitrogen is occasionally exhaled from 

 the lungs, in a sensible quantity, (Edwards,) and must come 

 from the decomposition of an azotised constituent of the blood. 



The fat of animals is a provision for the supply of oxidable 

 matter in respiration, and speedily disappears in the absence of 

 food, without a particle of it being discovered in the urine or 

 feces. Fat is most abundant in herbivorous animals, because 

 their supply of food from the vegetable kingdom ceases in 

 winter, and is a provision for their sustenance during that 

 period ; on the contrary the bodies of carnivorous animals in a 

 state of nature are entirely destitute of fat. (Liebig.) 



The following theory of respiration or of the action of oxygen 

 upon the blood, proposed by MM. Dumas and Boussingault, 

 has a high degree of probability. Under the influence of the 



