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ABSORPTION OF PROTEINS. 531
protein assimilation. This question of the absorption of proteins in
the intestine is still unexplained in many directions.
The extent of the protein absorption is dependent essentially upon
the kind of food introduced, since as a rule the protein substances from
an animal source are much more completely absorbed than from a
vegetable source. As proof of this the following observations are
given: In his experiments on the utilization of certain foods in the intes-
tinal canal of man, Rubner found that with an exclusively animal diet,
on partaking of an average of 738-884 grams of fried meat, or 948 grams
of eggs per day, the nitrogen deficit with the excrement was only 2.5-2.8
per cent of the total nitrogen introduced. With a strictly milk diet
the results were somewhat unfavorable, since after partaking of 4100
grams of milk the nitrogen deficit increased to 12 per cent. The con-
ditions are quite different with vegetable food, as shown by the re-
searches of Meyer, Rubner, Hultgren and Landergren, who made
experiments with various kinds of rye bread and found that the loss of
nitrogen through the feces amounted to 22-48 per cent. Experiments
with other vegetable foods, and also the investigations of Schuster,
Cramer, Meinert, Mori,1
and others on the utilization of foods with
mixed diets, have led to similar results. With the exception of rice,
wheat bread, and certain very finely divided vegetable foods, it is found
in general that the nitrogen deficit by the feces increases with a larger
quantity of vegetable material in the food.
The reason for this is manifold. The large quantity of cellulose
frequently present in vegetable foods impedes the absorption of pro-
teins. The greater irritation produced by the vegetable food itself or
by the organic acids formed in the fermentation in the intestinal canal
causes a more violent peristalsis, which drives the contents of the intes-
tine faster than otherwise along the intestinal canal. Another and most
important reason is the fact that a part of the vegetable protein sub-
stances seems to be indigestible, and because of the difficultly digestible
vegetable food, a large quantity of digestion fluids containing nitrogen
is secreted.
In speaking of the functions of the stomach we stated that after
the removal or excision of this organ, an abundant digestion and absorp-
tion of proteins may take place. It is therefore of interest to learn how
the digestion and absorption of proteins go on after the extirpation of
the second protein-digesting organ, the pancreas. In this connection
1
Rubner, Zeitschr. f. Biologie, 15; Meyer, ibid., 7; Hultgren and Landergren,
Nord. med. Arch., 21; Schuster, in Voit’s " Untersuch. d. Kost," etc., 142; Cramer,
Zeitschr. f. physiol. Chem., 6; Meinert, " Ueber Massennahrung," Berlin, 1SS5; Kell-
ner and Mori, Zeistchr. f. Biologie, 25.
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