830 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
ticularly one finds not only the needed apparatus but (what is no less 
important) trained assistants and servants, so that one is relieved of 
much of the time-consuming and disagreeable detail of experimenting, 
which is so much of an obstacle with us. 
THE QUANTITIES OF DIGESTIBLE SUBSTANCES IN FOOD. 
The first question we have now to ask may be put in this way: What 
proportion of each of the nutrients in different food materials is actu- 
ally digestible ? In a piece of meat, for instance, what percentage of 
the total protein and fats will be digested by a healthy person and what 
proportion of each will escape digestion ? The proportions of food 
constituents digested by domestic animals has been a matter of active 
investigation in the European agricultural experiment stations during 
the past twenty years. Briefly expressed, the method consists in weigh- 
ing and analyzing both the food consumed and the intestinal excretion, 
which latter represents the amount of food undigested. The difference 
is taken as the amount digested. 
Such experiments upon human subjects, however, are rendered much 
more difficult by the fact that in order that the digestibility of each 
particular food material may be determined with certainty we must 
avoid mixing it with other materials ; hence the diet during the exper- 
iments must be so plain and simple as to make it extremely unpalat- 
able. An ox will live contentedly on a diet of hay for an indefinite time, 
but for an ordinary man to subsist a week on meat, or fish, or potatoes, 
or eggs is a very different matter. NTo matter how palatable such a 
simple food may be at first, to a man used to the ordinary diet of a 
well-to-do community, it wfill almost certainly become repugnant to him 
after a few days. In consequence the digestive functions are disturbed 
and the accuracy of the trial is impaired, a fact, by the way, which 
strikingly illustrates the importance of varied diet in civilized life. 
For instance, in an experiment conducted in the physiological labor- 
atory at Munich by Dr. Rubner, the subject, a strong healthy Bavarian 
laboring man, lived for three days upon bread and water, a diet the 
monotony of which was much more endurable than one of meat or fish 
or almost any other single food material would have been. He was able 
to eat 1,185 grammes (about 21 pounds and 10 ounces) of bread per day. 
This contained 670 grammes of carbohydrates, mainly starch, of which 
only about grammes, or a little less than 1 per cent., escaped digestion. 
In this case, therefore, about 99 per cent, of the carbohydrates of the 
bread was digested. The bread contained 13 grammes of protein, of which 
13 per cent, was undigested, and 87 per cent., or seven-eighths of the 
whole protein, digested. The quantity of fatty matters in the bread 
was too small to permit an at all accurate test of their digestibility. In 
another experiment the digestibility of meat (beefsteak) was tested. 
The man consumed a little less than 2 pounds per day, but though it 
was cooked with butter, pepper, salt, and onions, so as to make it taste - 
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