276 ITS BEARING ON MEDICAL PRACTICE. 



4. Dr. E. Smith 5. 32 miles. 



5. Prof. Frankland 5. 47 miles. 



6. Dr. Murie 6, 53 miles. 



Mean 5, 952 miles. 



This result agrees very closely with the calculation already made from 

 760 grams of carbonic acid, in the case of Dr. Ranke, viz, 6.609 miles. 



WorJc due to animal heat. 



ANIMAX,S. 



1. Guinea i)ig 11. 05 milfs. 



2. Dog, (fasting) 5. 03 miles. 



3. Dog, (overfed) 14, 62 miles. 



Mean 10. 233 miles. 



SOI UCE OE MUSCULAR WORK. 



As soon as it was sal '.factorily established by Lavoisier and his suc- 

 cessors that the natural combustion of carbon and hydrogen in the blood 

 was sufhcient, or somev iiat more than sufficient, to account for the ani- 

 mal heat, it became a l. itter of great interest to physiologists to ascer- 

 tain, if possible, how mii;-li of the work developed in the blood by chem- 

 ical changes is employed in producing animal heat, how much in 

 mechanical work, external and internal, and how much in vital or mental 

 operations. 



At the outset of this inquiry, it received a misdirection from the con- 

 jecture thrown out by Liebig, that the excretion of nitrogen (in the form 

 of urea) gave necessarily the measure of the wear and tear of the mus- 

 cular tissues themselves, which are composed of proteinic or nitrogenous 

 compounds. This conjecture led to Liebig's celebrated classification of 

 food into heat-producing and flesh-forming foods, which has been unhes- 

 itatingly received until lately, in this country, by physiologists and 

 physicians. Before investigating the truth or falsehood of Liebig's 

 theory, it is worth while to state the most recent results obtained as to 

 the muscular work per day of which man is capable. 



From numerous observations, of which some were made by myself, on 

 ihe daily labor of hodmen, paviors, navvies, and pedlars, I have obtained 

 the following mean : 



Daily labor of man = 353.75 foot-tons = 109549 kilometers. 



This quantity of work is the exact equivalent of the work done by a 

 man of 150 pounds weight in climbiug through one mile of vertical 

 height, and is, as I have already shown, about one-sixth part of the 

 work expended in producing and maintaining animal heat. 



I was led to believe, from investigations made to determine the quan- 



