6 7 8 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 booh 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 elimi- 

 nated 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 



Ou 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 experi- 

 ments 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 do<i 



On a purely animal diet being 53"2 grammes. 



On a mixed diet " 325 " 



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 



