Page:Popular Science Monthly Volume 22.djvu/696

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678

THE POPULAR SCIENCE MONTHLY.

are proposing to spend the clay at home in finishing the diagrams, or tables, which you are going to use to-morrow at the hospital in your lecture on eatables, and which are now very much in the way when I want to see the pictures on the walls, or to take a book from a book-case. What you have taken would not enable you to do my work.

M. I am not so sure of that. At all events I am quite sure of this—that you are not wise in eating so much lean meat, in picking out every scrap of fat, and in taking no butter.

C. I want muscular power, and I feed my muscles by eating lean meat, which is muscle. I am right, so far, I suppose?

M. The muscle must no doubt be fed to enable it to act, but you are not at liberty to suppose, as you do, that the amount of urea and other excrementitious nitrogenous matter in the urine supplies the measure of the waste of muscle in muscular action which has to be repaired by food. You must seek this measure, not in the amount of urea eliminated by the kidneys, but in the amount of carbonic acid exhaled in the process of respiration; and the facts with which you have to do go to show that, after all, this food you are taking may not be that which is most suited to your wants to-day. As is shown in one of the experiments in which Pettenkofer was assisted by Voit, and as you may see in one of the tables which hide the pictures and books here—thus, No. 1—the difference between a day of rest and a day of hard work, as regards the elimination of carbonic acid and urea, is marked not by an increase in the quantity of urea, but by an increase in the quantity of carbonic acid, the actual quantities being—

Grammes of carbonic acid. Grammes of urea.
On a day of rest 911·5 37·2
On a day of hard work 1,184·2 37·

On the day of hard work there is a very marked increase in the quantity of carbonic acid, and a trifling decrease in the quantity of urea. What do you say to this fact? Again: As is shown in one of the experiments of Lehmann, and as you may see in this table, No. 2, the amount of urea eliminated by the kidney is, in the main, proportionate to the amount of nitrogenous matter contained in the food; the result of feeding a dog

On a purely animal diet being 53·2 grammes.
On a mixed diet " 32·5 "
On a vegetable diet " 22·5 "
On a non-nitrogenous diet, consisting of fat or grape-sugar or starch 15·4 "

Once more: As is shown by Edward Smith in an experiment upon himself, and as you may see in this table, No. 3, the amount of carbonic acid given off every minute is in direct proportion to the amount of work done in the time, the actual amount being—