
84 STORRS AGRICULTURAL EXPERIMENT STATION. 
undigested residue of the food, and of the so-called metabolic 
products. ‘The latter consists mainly of residues of the diges- 
tive juices. Later research has shown that in man the actual 
amount of undigested nutrients makes up relatively a much 
smaller portion of the intestinal excretion than was formerly 
supposed. Indeed some investigators are inclined to take the 
ground that the nutrients in ordinary food materials, properly 
prepared, are almost wholly digested by persons in health, and 
that the solid excreta are almost entirely made up of the so- 
called metabolic products and residues from the alimentary 
canal.* While the feces do not give an exact measure of 
either the actual amount of the different nutrients which re- 
main undigested in their passage through the alimentary canal 
or of the amounts of digestive juices used for the digestion, 
they do give us a measure of the availability of the food for 
use in the body. - If the same quantities of two different food 
materials require the same amounts of digestive juices to pre- 
pare them for absorption, but the first is more completely 
digested, z. e., leaves less undigested residue than the second, 
the first is more available. So likewise if both are equally 
digestible but the former requires more of the digestive juices 
to digest it, it may be regarded as really supplying a less 
amount of available material to the body. 
The experimental data as to the digestibility of different 
kinds of nutrients in different classes of food materials are as 
yet limited. There are on record a considerable number of 
digestion experiments with men. In some of these single food 
materials were used. In others an ordinary mixed diet of 
more or less varied character was employed. ‘The experiments 
with single food materials or with very simple mixed diet give 
data for estimating the coefficients of ‘availability of the nutri- 
ents of individual food materials. From such data we have 
prepared tentative coefficients for the availability of the nutri- 
ents of a number of the more common kinds of food materials 
such as meats, milk, wheat bread, potatoes, etc. It is, how- 
ever, a question whether these coefficients could be correctly 
applied to the same food materials when they are eaten in the 

* See discussion of this subject in Storrs Reports, 1896, p. 163 and 1897, p. 154. This 
matter will also be discussed in more detail in a future bulletin of the Office of Exper- 
iment Stations of the U. S. Department of Agriculture. 
