Page:Popular Science Monthly Volume 1.djvu/323

Rh though evacuation increased, the amount of urea was diminished. White wheaten bread gives least excreta. The proportion of water contained in this matter affords the means of judging how long it had remained in the intestine, and how far the process of extracting the nutritive properties had gone. The substance evacuated in small quantity after a meal of flesh-meat contains hardly any remains of meat and 50 per cent, of solid matter, while the excreta from bread-food, evacuated in greater quantity, with much of the bread not transformed, has only 23 per cent, solid matter.

It might be supposed that the yeast in the bread is the cause of this; but Meyer has shown that a ration of starch-pudding and unleavened bread gives residuum in equal proportion with leavened bread. He has also shown that bread, into the composition of which enter nutritive salts, according to the Horsford process, gives a residuum equal to that of common bread. The result, therefore, is not due to the absence of these salts from bread. Dr. Bischoff has shown, in the course of some experiments he made at the instance of Liebig, that the addition of extract of meat, with or without salt, to the bread given to a dog, does not affect the intestinal absorption, nor does it lessen the amount of excrementitious matter. The objection might perhaps be urged that, as the dog is purely carnivorous, experiments made on him will not warrant a universal conclusion. Therefore, Dr. Hoffmann made the same experiment with a man. The man was fed on potatoes, pulse, and bread, and there were then 116 parts of dry excreta; when extract of meat was added, there were still 109.

According to Haubner, the addition of a little peas to potatoes notably diminishes or even entirely dissipates the starch, which else is found in great quantity in the excreta of sheep. This result he attributes to the influence of the albumen in the peas. Dr. Bischoff gave a dog 800 parts of bread and 100 of meat. The amount of residuum was not lessened, nor the assimilation of the bread increased. Dr. Meyer found a dog, on 1,000 parts of bread, to give TO of excreta; on 1,000 of bread and 100 of meat, 66 parts; and on 1,000 of bread and 300 of meat, 75 of solid residue. There is, then, no means of promoting the digestion of bread or potatoes, or other vegetable food, in the intestine whether of man or of dog, nor of preventing the loss of the starch.

From the persevering observations of Dr. Hoffmann, it follows that this imperfect digestion and this voluminous excretion are unavoidable a fact which, on a vegetable diet, necessitates larger consumption, even though each of the elements were in itself capable of absorption. If a man consumes in a day 1,000 parts potatoes, 207 lentils, 40 bread and beer, he takes in 14.7 of nitrogen. Of the latter he gives out 7 by the kidneys, and 6.9 in 116 of dry excreta. The latter contain 24 per cent, of the dry food, and 47 per cent, of the nitrogen. But, when he takes in animal food, the same amount of azote and of