PO UL TR T- CRAFT. 1 1 1 



It is said that an excess of carbohydrates pours through the system undigested. 

 That supposition is contrary to the known effects of feeding heavily of carbon- 

 aceous matter. The immediate consequence of feeding fat to excess is scour- 

 ing. Some authorities on feeding say all the protein taken into the system is 

 used : i. e. an excess of protein is impossible. But this is not in accordance 

 with practical experience in feeding " narrow" or highly nitrogenous rations. 

 Experience teaches that such rations cause digestive troubles as surely, if not 

 as quickly, as an excess of fats. 



152. Food Values. There are two standards of measurements of food 

 values : 



(i). The measurement of quality, of proportionate value of principal ele- 

 ments : NUTRITIVE RATIO. 



(2). The measure of bulk, of content, of degree of concentration, of total 

 heating capacity : POTENTIAL ENERGY. 



The NUTRITIVE RATIO of a food (single article or mixture) is the ratio of 

 its proteids to its carbohydrates and fats, reduced to terms of carbohydrates ; 

 one part of fat by weight having a fuel value two and one-half times as great 

 as an equal weight of carbohydrates. The chemical analysis of a food being 

 known, the nutritive ratio is determined thus, taking corn as the example : 



Corn (see table, f 153) contains 10.4 parts protein, 70.3 parts carbohydrates, 

 5 parts fat : its nutritive ratio is : 



10.4: 7o-3+(5X2.5) = i: 7.9. 



The POTENTIAL ENERGY of a food is the gross fuel value of its digestible 

 matter. It is expressed in calories per ounce. A calory is the amount of 

 heat required to raise one gram of water one degree centigrade. One ounce 

 of carbohydrates or protein has a potential energy of one hundred and sixteen 

 calories. One ounce of fat has a potential energy of two hundred and sixty- 

 four calories. The potential energy of any food substance of which the 

 chemical composition is known is calculated thus, taking corn again as the 

 example, and using the figures in the table as percentages of an ounce : 

 ( 264 X. 05) -K-703-)-. 1 04) 116 = 106. 



The nutritive ratio and potential energy of each single article may, when 

 computing values of compound foods, or of rations, be regarded as constant 

 quantities. As a matter of fact, they vary greatly in different samples of the 

 same article, but calculations from the figures in the table, which are averages 

 of a large number of analyses, may properly be assumed to give the average 

 and usual values of the different foods. 



The values of a ration vary with its ingredients, and are calculated from 

 averages of the values of the ingredients. (See ^158). 



