UREA AND MUSCULAR WORK. 429 



sate ,1 for afterwards by a diminished urea excretion. Thus, 

 hourly, before the ascent Fick and Wislecenus each ex- 

 creted on the average about 4 grams (62 grains) of urea; 

 during the ascent between 7 and 8 grams (108-124 grains); 

 but during the subsequent 16 hours, when any urea formed 

 in the work would certainly have reached the urine, only 

 an average of about 3 grams (46.5 grains) per hour. 



It may still be objected, however, that a good deal of the 

 muscle work may be done by the energy of oxidized muscle 

 proteid; that the amount of this oxidation occurring in a 

 muscle during rest or ordinary work is pretty constant and 

 simply takes different forms in the two cases, much as a 

 -steam-engine with its furnace in full blast will burn as 

 much coal when resting as when working, but in the former 

 oase lose all the generated energy in the form of heat, and 

 in the latter partly as mechanical work. Thus the want of 

 increase in urea during muscular activity would be explained, 

 while still a good deal of utilizable energy might come from 

 proteid degradation. But if this were so, then the work- 

 ing Body should eliminate no more carbon dioxide than the 

 resting; the amount of chemical changes in its muscles 

 being by hypothesis the same, the carbon dioxide eliminated 

 should not be increased. Experiment, however, shows 

 ihat it is, and that to a very large extent, even when the 

 work done is quite moderate and falls within the limits 

 which could be performed by the normal proteid degrada- 

 tion of the Body. Quite easy work doubles the carbon 

 dioxide excreted in twenty-four hours, and in a short period 

 of very hard work it may rise to five times the amount 

 eliminated during rest. Since the urea is not increased, or but 

 very slightly increased, at the same time, this carbon dioxide 

 cannot be due to increased proteid metamorphosis; and 

 it therefore indicates that a muscle works by the oxidation 

 of carbonaceous non-nitrogenous compounds. Since all 

 the carbon compounds oxidized in the Body contain hydro- 

 gen this element is also no doubt oxidized during muscu- 

 lar work; but its estimation is difficult and has not been 

 attempted, because the Body contains so much water ready 

 .formed that a large quantity is always ready for increased 



