OXIDATION. 907 



and pulmonary excretions, in the Herbivora, viz., 25 to 1, as compared 

 with the urine; but in the Carnivora, the proportions in the urine, as 

 compared with the breath, are reversed, being as 3.25 to 1. The 

 nitrogen, in the Carnivora, passes almost exclusively into the urine, 

 the proportion to that in the skin and lungs being as 99 to 1 ; in the 

 Herbivora, the ratio is only as 1.5 to 1. The excreta in a Carnivor- 

 ous animal, represent also the excreta of an animal fed on a pure flesh 

 diet ; but those of an Herbivorous animal exhibit the results of an ex- 

 cess in the proportion of the carbhydrates, viz., an increased activity 

 of the pulmonary and cutaneous exhalations. 



It must further be observed that the quantities of the albuminoid 

 substances, or their derivatives, removed in a solid form from the body, 

 in the mucous and unused secretions of the digestive canal, in the 

 epithelium, from other mucous membranes, and with the epidermis, 

 nails, and hair, are very small, and escape all active metamorphosis. 



Finally, the sum of all the chemical changes in the body, is oxida- 

 tion. The carbon of all the carbhydrates and hydrocarbons, appears 

 as carbonic acid, and their bydrogen and oxygen, as water. A portion 

 of the carbon, hydrogen, and oxygen, of the decomposed albuminoid 

 bodies, also appears in the excreta, as carbonic acid and water ; but a 

 considerable portion of these elements with the nitrogen, is discharged 

 in the form of urea. The sulphur and phosphorus produce their 

 respective oxygen acids. For these changes, a larger amount of 

 oxygen, beyond that contained in the body, is needed ; and this is 

 supplied by the atmosphere in respiration. It has been computed, that 

 100 parts of dried meat require 167 parts, by weight, of oxygen, for 

 their disintegration in the body. The results appear as 182 parts of 

 carbonic acid, 52 of water, and 31 of urinary products ; whilst only 

 2 parts escape unchanged from the alimentary canal. No pure carbon, 

 hydrogen, or nitrogen, is evolved from the body, but only chemical 

 combinations of these elements, with oxygen, or with each other. 

 Ammonia is one of these. The minute quantities of carburetted and 

 sulphuretted hydrogen, sometimes disengaged, are probably direct pro- 

 ducts of the decomposition of the food, and not the results of vito- 

 chemical processes. Of the carbon, 8.8 oz. are evolved as carbonic 

 acid from the lungs, nearly 0.1 oz. from the skin ; 0,34 oz. escape by 

 the urine, and 0.71 oz. by the solid excreta. All the nitrogen appears 

 in the two latter excretions, 0.56 oz. in the former, and 0.1 oz. in the 

 latter. 



The so-called respiratory, calorific, or heat-giving, elements of the 

 food, chiefly enter the blood, and there undergo oxidation ; whilst the 

 plastic, histogenetic, or tissue-forming elements, unless taken in ex- 

 cess, first build up the blood corpuscles and the solid tissues, and then 

 undergo oxidation ; but these latter in reality contain fat and often 

 sugar, which may be immediately oxidized in the blood ; and so even 

 an albuminoid diet may, in that case, act as respiratory food. This 

 must be the case in starving men and animals, in animals fed on a 

 pure flesh diet freed from fat, and, to a certain extent, in all Carnivora. 

 On the other hand, the carbhydrates are probable sources of fat ; and 

 fatty matter is essential to plastic or histogenetic processes. The 



