FOOD OF MAN. 545 



nitrogen. Great light has been thrown on this subject, in recent pe- 

 riods, by the labours of the organic chemist. These have shown, that 

 the chief proximate principles of animal tissues, and those that have 

 been regarded as highly nutritious amongst vegetables, have almost 

 identically the same composition; and are modifications of protein. 1 

 The following tables from Liebig 2 exhibit the striking similarity in con- 

 stitution, and in the proportion of constituents, of different animal and 

 vegetable compounds of organization. 



jUnimal proximate principks, according to Mulder. 



Albumen. Fibrin. Casein. 



Carbon, . 54-84 54-56 54-96 



Hydrogen, 

 Nitrogen, 

 Oxygen, . 

 Sulphur, . 

 Phosphorus, 



6-90 



15-72 



22-13 



0-33 



0-36 



7-15 

 15-80 

 21-73 



0-36 



100-00 100-00 100-00 



Vegetable proximate principles, according to Scherer and Jones. 



Albumen, from wheat. Fibrin. Casein or Legumin. 



Carbon, .... 55-01 . . 54-603 . . 54-138 



Hydrogen, . ... 7-23 . . 7-302 . . 7-156 



Nitrogen, ... 15'92 . . 15-809 . . 15-672 

 Oxygen, ~) 



Sulphur, ^ . . 21-84 . . 22-286 . . 23-034 

 Phosphorus, j 



100-00 100-000 100-000 



As the different parts of organized bodies contain a considerable 

 portion of nitrogen, a question has arisen regarding its source ; some 

 believing, that it is obtained from the food, others by respiration. 



M. Magendie 3 instituted experiments with the view of determining 

 the nutritive qualities of non-nitrogenized substances. They consisted 

 in feeding animals, for the necessary time, on a diet whose chemical 

 composition was rigidly determined. He fed a dog, three years old 

 and in good condition, on pure white sugar and distilled water. For 

 seven or eight days, the animal appeared to thrive well, was lively, and 

 ate and drank with avidity. In the second week, it began to fall off, 

 although its appetite continued good, and it ate six or eight ounces of 

 sugar in the twenty-four hours. In the third week, it became ema- 

 ciated, its strength diminished, its gaiety was gone, and its appetite 

 impaired. An ulcer formed on each eye, at the centre of the cornea, 

 which subsequently perforated it, and allowed the humours to escape. 

 The emaciation, as well as loss of strength, went on progressively in- 

 creasing; and, although the animal ate daily three or four ounces of 

 sugar, the debility became so great, that it could neither chew, swallow, 

 nor execute the slightest movement. It died on the thirty-second day 

 of the experiment. On dissection, the fat was found to have entirely 



1 See page 47. 



* Animal Chemistry, Gregory's and Webster's edit., pp. 100, 283, and 301, Cambridge, 

 Mass., 1842. 



s Precis Elementaire, 2de edit. ii. 488, Paris, 1825. 



VOL. i. 35 



