CHEMICAL COMPOSITION 



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Vitamines are nitrogenous complexes, which are essential for the 

 growth or the Well-being of the organism. 



The food materials may therefore be classified into the great 

 tissue-forming protein, aided by salts and water, and the great heat- 

 energy producing carbohydrate and fats, aided by protein, and 

 essentials, the work of which is not understood — viz., vitamines 

 and lipoids. 



As the heat and energy can be expressed in terms of the calorie 

 (or large calorie written with a capital C), which is the amount of heat 

 necessary to raise the temperature of i kilogramme of water one 

 degree centigrade, and as protein is the essential tissue -former, it 

 follows that in calculations as to a diet two matters stand out — viz., 

 the quantity of protein in that diet, and the number of calories 

 which can be obtained therefrom. 



Water has a food value of i in i,ooo, and should be freely avail- 

 able, and salt is usually easily procurable, though we have lived in 

 parts of the tropics in which neither were easily obtained. 



Vitamines and lipoids we cannot measure, and at present we are 

 merely concerned with their presence. 



Therefore, from a practical point of view, the quantities which 

 require calculation are the amount of protein in a diet and the 

 number of Calories, and this brings us to the subject of quantity. 



QUANTITY. 



The only accurate method of determining the quantity of the 

 various food factors of any given diet is by means of the respiration 

 calorimeter, in which the work done, the heat generated, and the 

 waste products eliminated, are expressed in terms of the Calorie, 

 which, in energy, is the equivalent of 1-54 foot tons, or, in other 

 words, represents that amount of mechanical energy which is required 

 to raise i ton in weight 1-54 feet in height. 



When the respiration calorimeter is not available, the quantity 

 of the total food consumed by the person or persons under observa- 

 tion should be carefully weighed and records made. Then samples 

 of the various constituents of this diet should be analyzed, with the 

 view of determining the quantity of protein, carbohydrate, and fat 

 contained therein. 



With regard to the Calories produced by these various factors, 

 Rubner's experiments upon animals enabled him to enunciate the 

 so-called isodynamic law, which states that 227 grammes of protein, 

 or of carbohydrate, yield 930 Calories on consumption in the body, 

 and that this is the same as the heat so produced by 100 grammes of 

 fat, and therefore 227 grammes of protein, or of carbohydrate, are 

 isodynamic with 100 grammes of fat. In other words, i gramme of 

 protein produces the same amount of heat as i gramme of carbo- 

 hydrate — ^viz., 4-1 Calories, while I gramme of fat gives 9-3 Calories. 



It may, perhaps, be incidentally noted that i gramme of alcohol 

 produces 7-0 Calories. 



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