DIGESTIBILITY AND AVAILABILITY OF FOOD. 



243 



made elsewhere. The factors for availabihty of the nutrients 

 of total food of mixed diet suggested at that time are here 

 compared with the average of the results of all the experi- 

 ments included in the present report. The former are given 

 in round numbers. 



Proposed factors, 



Average of results here given, 



Protein. 



% 

 92.0 

 90.8 



Fat. 



% 

 95.0 

 95-3 



Carbo- 

 hydrates. 



% 

 97.0 

 97.6 



SUMMARY AND CONCLUSION. 



The purpose of the digestion experiments here reported zvas to 

 find what proportions of the proteiii, fats, carbohydrates, and 

 energy of ordijiary mixed diet, when eateii by healthy jnen, were 

 made available to the body. The results for the different nu- 

 trients were found by comparing the quajitity of each in the 

 original food material with the quantity of the corresponding 

 ingredient in the intestinal excreta. In the case of the energy, 

 that of the tinoxidized material of the uriiie was also taken iyito 

 accowit. The results expressed in pe^xentages are taken as the 

 w efficient ts of ava ila bility . 



These factors a?'e frequently called coefficients of digestibility. 

 It is a common practice to consider the solid excreta as represent- 

 ijig the i7idigestible portion of the food. This, however, is not 

 quite accurate, because the feces include, besides the imdigested 

 residues of food, the residjies of digestive juices, and other mate- 

 rials, so that the amounts of iyigredients in the feces are larger 

 than those of the portion of the food which escapes digestion, and 

 the proportio}is of digestible nutrients when calculated from total 

 food and total feces are thus made too small. Oji the other hand, 

 the total material of the feces does ?'epresent that zchich zvas un- 

 available to the body for the tzvo chief purposes of nutrition, the 

 building of tissue and the yielding of energy. It is therefore 

 more correct to apply the term availability to the difference be- 

 tzveen food and feces. But while this term is here preferred, the 

 term digestibility may also be used i?i deference to common cus- 

 tom; so long as the meaning is clearly understood it is of little 

 importance zvhich term is employed. 



