DIGESTIBILITY AND AVAILABILITY OF FOOD. 245 



7vas icsed in large quantities was as large as, or larger than in 

 the experiments in which the qtiantities zvere more nearly like 

 those i?i the ordinary diet. 



hi these experiments more or less severe muscular zvork had no 

 apparent effect up07i the availability of the different mitrients of 

 the diet. It made practically no difference whether the vien were 

 as quiet as possible, or were engaged in very light, or moderate, 

 or severe musctdar work, the proportiofis of tinavailable material 

 rejected by the ijitesti^ie were no larger in one case than in the 

 other. That is to say , so far as the usijig up of the mitrients of 

 the food zvas concerned, the amoiint of muscular exercise made no 

 appreciable difference. 



Although the mimber of experiments is large, there were not 

 enoiigh of them, nor were they m.ade with enoiigh different sub- 

 jects, nor were there enough kinds and combinatioiis of food ma- 

 terials to warrant final conclusions as to the average amounts of 

 mitrierits digested from ordinary diet by healthy men in geiieral; 

 at the same time the agreeme^it of the results with each other and 

 with those of other experiments implies that the general average 

 is 7iot very far from an indication of the availability of the nu- 

 trients of mixed diet when eaten by people in good health uiider 

 conditio7is which obtain in the United States. Accordi^igly it 

 would seem that zve shall not be very far out of the zvay ifi as- 

 su7ning that the coefficients of availability of the iiutrients of 

 mixed diet are: For protein, g2 per cent.; for fat, g^ per cent., 

 a7id for carbohydrates, gj per cent. That is to say, these figtires 

 77iay be take7i as representi7ig very 7iearly the proportio7ts which 

 are actually available to the body for the building of tissue a7id 

 the yielding of e7ie7gy . 



It is to be bor7ie i7i mind, hozvever, that these factors dcpe7id 

 conside7'ably upon the proportions of a7ii77ial and vegetable foods 

 i7i the diet, as the availability of the nutrients is different i7i dif 

 fere7it 77iaterials. Tlnis, the protein of ani77tal foods, like i7ieat 

 and milk, is 7nore completely digested a7id zitilized tha7i that of 

 most vegetable foods, like bea7is or potatoes. The availability of 

 the protein of m.ixed diet will therefore vary accordi7ig as it con- 

 tai7is a larger or S77ialler proportio7i of ani77ial food. Ro7ighly 

 speaki7ig, however, about 95-96 per ce7it. of the total orga7iic 7nat- 

 ter and 91-92 per cent, of the total energy of 7nixed diet will be 

 available. To put it in another way, the body rejects abo2it 5 per 

 ce7it. of the 7iutrie7its and about 9 per cent, of the energy of its food. 



17 



