832 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
Summary of results of experiments on the digestion of the constituents of meat and fish by 
a dog and by a man. Percentages undigested. 
Dog. 
Man. 
Food. 
Meat and 
lard. 
Fish and 
lard. 
Meat, but- 
ter, etc. 
Fish, but- 
ter, etc. 
Water-free substance, apparently undigested 
Per cent. 
3.4 
Per cent. 
3.2 
Per cent. 
4.3 
Per cent. 
4.9 
Nitrogen (protein) from meat or fish, apparently un- 
digested 
2.2 • 
1.6 
2.5 
2.0 
Nitrogen (protein) from meat or fish actually undi- 
gested 
0.3 
0.0 
0.7 
0. 5 
Fat, mostly from lard or butter, apparently undi- 
gested 
2.8 
3.0 
5.2 
9.0 
Asb, apparently undigested 
14.3 
14.1 
21.5 
" 22. 5 
Practically all the protein of both the fish and lean beef were digested 
by the dog, and all but oue-half or three-fourths of 1 per cent, by the 
man ; these results agree with what would be expected from the nature 
of the nitrogen compounds and what is known of the laws of digestion 
and absorption, and leave little doubt that practically all of the protein 
of both will be digested by a healthy organism under normal conditions. 
The conclusion that the flesh of the common kinds of fish agrees very 
closely in digestibility with that of the common kinds of meat, at least 
so far as the protein (the chief constituent of the “lean” of meat and 
fish) is concerned, seems equally well grounded. It would seem from 
other considerations (especially from actual experiments with meats, in 
which the fat is imperfectly digested) that fish, having generally less 
fat than meat, is more easily and completely digested. 
It is interesting to note how different food materials compare in 
digestibility as shown by experiments such as those just described. 
Results of such trials are given in Table n of the previous chapter. 
The amounts of fat in the vegetable foods are so small that the ex- 
periments do not tell exactly what proportions are digested. The meats 
and fish contain practically no carbohydrates. The digestibility of the 
carbohydrates (sugar) of milk was not determined ; those of the vege- 
table foods, except the beets, were almost completely digested. That 
the protein of cow’s milk should be so much less completely digested 
than that of meat seems a little strange. Children digest a little more 
than adults. Dr. Camerer found his boys and girls of from 2 to 12 
years of age to digest from 91 to 97 per cent, of the protein of cow’s 
milk, while grown men in experiments by Dr. Rubner digested from 88 
to 94 per cent. But in experiments in which milk and cheese were 
eaten together by a man, in Dr. Rubner’s experiments, all or nearly all 
of the protein of both was digested. The percentages of fats of milk 
digested were practically the same with adults as with children. It is 
noticeable that both children and adults digest only about half of the 
mineral salts of the milk. Why so much of the fats of the meat, from 
a twelfth to a fifth, should fail to be digested it is not easy to say. 
Some food materials, as meat, bread, and milk, have been tested by 
