370 STUDIES IN ADVANCED PHYSIOLOGY. 



so give rise to the liberation of new energy, carbon dioxide 

 and water being the result, as in the first case, but the ni- 

 trogenous remnant being again saved and by combination 

 with new fats or sugars and the oxygen from the lungs, be 

 built for a second, a third, or fourth time into living tissue. 

 If this view is correct it would explain why the loss in nitro- 

 gen does not vary with the work, a man resting eliminating 

 from his body about as much as a man working. 



When it is said that the nitrogenous remnant is saved, 

 there is to be added that a small portion of this nitrogenous 

 remnant, however, is lost; some possibly accidentally car- 

 ried away by the circulating fluid, some possibly chemically 

 unfit to be used again. It is this little loss, this wear and 

 tear, which is sent to the liver and in the liver is burned 

 into urea and then eliminated from the kidney. But this 

 wear and tear may almost be as much in a resting person 

 as in an active person, just as the wear and tear of an en- 

 gine that is in proper use may not exceed the wear and tear 

 of an engine standing idle on the sidetrack. 



Some interesting experiments have been made showing 

 that the loss of the nitrogen from the body is not at all 

 proportional to the work done. Persons have ascended 

 mountains and during the period of such exertions, as well 

 as before and after, careful quantitive determinations were* 

 made of the amount of urea eliminated from the kidneys. 

 It was found that even in such laborious work as mountain 

 climbing the nitrogenous loss from the body was not pro- 

 portionately larger, in fact hardly materially larger than the 

 loss while resting. On the view just given of the manner 

 in which the nitrogen is used over and over again this is 

 readily understood. 



The amount of carbon dioxide produced, and of course 

 the water, is however, directly proportional to the amount 

 of work done. At each chemical disintegration a certain 

 amount of carbon, oxygen and hydrogen is lost, which must 

 be replaced in the next constructive process by an equal 

 amount of new material. Evidently, therefore, the amount 



