DIGESTIBILITY AND AVAILABILITY OF FOOD. l8l 



the body for the building and repair of tissue and the yielding 

 of energy, and have been so used in previous reports of the 

 Station. 



In accordance with the above explanation, the available nu- 

 trients of food are found by subtracting the total amounts in 

 the feces from the total amounts in the food. In like manner, 

 the digestible nutrients, that is, the amounts actually digested, 

 would be found by subtracting the total amounts in the un- 

 digested residues from the total amounts in the food. The 

 difference between the available nutrients and the digestible 

 nutrients would thus be represented by the amounts corre- 

 sponding to the metabolic products. 



In deference to common usage we here emplo}^ the word 

 "digestible" in some cases as synonymous with "available" 

 but with a very definite understanding that such use of the 

 term "digestible" and the corresponding term "digestibility" 

 is not exactly accurate. 



The digestion experiments here reported form part of the 

 metabolism experiments with man in the respiration calorim- 

 eter. As has been explained in preceding reports, the data of 

 the metabolism experiments include statistics of the amounts 

 of nutrients consumed in the food and excreted in the feces. 

 Furthermore, each metabolism experiment or series of experi- 

 ments is preceded by a preliminary period in which the subject 

 while outside the respiration chamber receives the same kind 

 of diet, and the amounts of nutrients in the food and feces are 

 determined. The data thus secured give important informa- 

 tion regarding the digestibility and availability of the nutrients 

 of mixed diet. 



Subjects. — Three different men served as subjects of the ex- 

 periments. They were all young, active, in excellent health, 

 their digestion was apparently normal, and they did not find 

 the conditions of the experiment irksome. E. O., an assistant 

 in the laboratory, was a Swede who had lived a number of 

 years in this country. He was 32 years old, and weighed 

 about 70 kilograms (154 pounds). J. F. S., a chemist assist- 

 ing in conducting the metabolism experiments, was a Cana- 

 dian, 29 years old, and weighing about 65 kilograms (145 

 pounds). J. C. W. was a college student, an American, 22 

 years of age and weighing about 80 kilograms (176 pounds). 



13 



