l8o STORRS AGRICULTURAL EXPERIMENT STATION. 



which are digested and made available to the body for the chief 

 purposes of nutrition, i. e., the building of tissue and the 3'ield- 

 ing of energy. The methods pursued in the experiments and 

 the ways in which the results are interpreted have been ex- 

 plained in previous reports.* A brief recapitulation will there- 

 fore suffice here. 



Of the total food eaten, the larger part is digested, but small 

 portions escape the action of the digestive juices and are ex- 

 creted in the feces. Along with this undigested residue of the 

 food there is in the feces a certain amount of other material 

 making up the so-called metabolic products. These metabolic 

 products consist largely of the residues of the digestive juices 

 which have been poured into the alimentary canal and not re- 

 absorbed. The}' contain, however, more or less of other ex- 

 cretory products. Taken together they represent a part of the 

 cost of the digestion of the food. 



In the stricter sense, the digestible portion of the food is 

 that which is actually taken into the circulation; it would be 

 found by subtracting the undigested residues from the total 

 food. Thus far, however, no satisfactory and convenient 

 method has been devised for separating the undigested resi- 

 dues from the metabolic products in the feces, consequently 

 the actual digestible portion of the food cannot be easily de- 

 termined. But the real object of such digestion experiments 

 as are here reported is to find what proportion of food and its 

 several ingredients is actually made available to the body; and 

 as the whole material of the feces, including the undigested res- 

 idue and metabolic products, is, in this sense, unavailable, the 

 difference between the amounts of the several constituents of 

 the feces and the corresponding constituents of the food, which 

 apparently represents the digestibility, actually represents the 

 availability of the food. In discu.ssions of this .sort the words 

 digestible and digestibility are commonly applied to the amounts 

 which are thus made available; that is to say, they represent 

 the difference between total food and total feces; but inasmuch 

 as this difference represents not the total amounts digested but 

 the amounts digested minus the metabolic products, the use of 

 these terms is not entirely accurate. Instead of the above the 

 terms available and availability have been suggested as express- 

 ing more exactly the quantities which are actually utilized by 



* Report for 1896, p. 163 and 1897, p. 154. 



