130 PHYSIOLOGICAL CHEMISTRY. 



Such a diet affords the best means of ascertaining the absolute and 

 relative quantities of the different ingredients required for food. If we 

 take the average composition of meat and bread, and estimate their 

 albuminous, starchy, and saline matters, together with the water con- 

 tained in both solid and liquid food, we find that the daily ration is 

 composed nearly as follows : 



Albuminous matter ...... 130 grammes. 



Starch and sugar ...... 300 " 



Fat ..... 100 



Mineral salts ....... 20 " 



Water ........ 2,000 



Of the mineral salts, nearly eight grammes are naturally contained 

 in the substances used for food and drink ; the remainder consists of 

 sodium chloride, artificially added to the food, or used in its preparation. 



The proportion in which the albuminous and the non-nitrogenous 

 principles should be mingled in the food is of considerable importance, 

 and this proportion has been determined within very accurate limits. 

 In making such an estimate it is necessary to include the carbohydrates 

 and fats under the same head ; but the fats are properly regarded as 

 having a different alimentary value from the carbohydrates. This de- 

 pends on the fact that the final result of the transformation in the liv- 

 ing body of all the non-nitrogenous substances is carbonic acid and 

 water, thus representing a process of oxidation, the necessary oxygen 

 for which is introduced with the inspired air. But the capacity for 

 oxidation of the fats is greater than that of the carbohydrates, as shown 

 by the relative proportion of their constituent elements. 



The composition, by weight, ( 2 



f 4 K /nir A\- < H 10 or in 100 parts. H 6.17 



of starch (0 6 H 10 6 ) 1S | o ^ Q 49 . 36 



102 100.00 



Here the oxygen is already present in sufficient proportion to satu- 



rate all the hydrogen by the formation of water ; while the 44.47 parts 



of carbon will unite with 118.58 parts of oxygen to form carbonic acid. 



On the other hand, if we take palmitine as representing the average 



constitution of the fats, we have 



The composition, by weight, (2. 61 ^ 



#-A*5nwr -<H 98 or in 1 00 parts. H 12.15 



of fat (0 51 H 98 C ) ls 



806 100.00 



Here the oxygen is present in much diminished proportion ; and, for 

 complete oxidation of the fat, to form carbonic acid and water, the 75.93 

 parts of carbon will require 202.48 parts of oxygen, and the 12.15 parts 

 of hydrogen will need 85.28 additional, over and above the 11.92 parts 

 of oxygen already present. Thus the quantities of oxygen appropriated 

 during complete oxidation, by starch and fat respectively, are as fol- 

 lows: 



