328 FUNCTIONS OF NUTRITION. 



urea. The alcoholic solution is then filtered and evaporated until the 

 urea separates in a crystalline form.* 



The quantity of urea in a given volume of urine is ascertained by 

 decomposing it, according to Davy's method, with a solution of sodium 

 hypochlorite. A narrow graduated glass tube, open at one extremity, 

 with a capacity of about 50 cubic centimetres, is filled to a little more 

 than one-third its height with mercury, upon which are poured 3 or 4 

 cubic centimetres of the urine to be examined. The remainder of the 

 tube is then filled with the sodium hypochlorite solution, its mouth 

 closed, the fluids well mixed by agitation, and the tube inverted in 

 a shallow dish filled with a saturated solution of sodium chloride. 

 The mixture of urine and hypochlorite solution remains in the tube ; 

 and as the urea is decomposed, its nitrogen collects in the upper end of 

 the tube, where its volume may be read off on the scale, after the action 

 has ceased. Every cubic centimetre of nitrogen, thus disengaged, rep- 

 resents 2.5 milligrammes of urea. 



The results obtained by nearly all experimenters led to the conclu- 

 sion that the quantity of urea excreted is especially increased by mus- 

 cular exertion, until a doubt was thrown on this point by Pick and 

 Wislicenus in 1866. These observers ascended a mountain on foot, the 

 ascent occupying a little over eight hours ; during which time, "and for 

 seventeen hours beforehand, they confined themselves to a diet of non- 

 nitrogenous food. They found the hourly amount of urea discharged 

 less during the ascent than it was before ; but it increased during the 

 following night, after a meal of animal food. 



Subsequent observers have obtained various results. Parkes,f in a 

 series of extended observations, found that the discharge of urea was 

 increased not during, but after, a period of muscular work. This was 

 shown even in a man confined for five days to a non-nitrogenous diet, 

 in whom the discharge of urea was not increased on the day of unusual 

 muscular effort, but on the following day was a little more than doubled. 



The observations of Flint, J in the case of the pedestrian Weston, 

 have the advantage of extending over comparatively long periods, both 

 of exercise and rest, the diet remaining unchanged in general character. 



The pedestrian was under observation for fifteen days ; namely, five 

 days previous to the walk, five days during its continuance, and five 

 days immediately afterward. For the period preceding the walk, the 

 average exercise was about eight miles per day ; during the walk it 

 was nearly sixty-four miles per day, and for the subsequent period a 

 little over two miles per day. The results obtained represent accord- 

 ingly the amount of urea excreted under ordinary conditions, that dis- 

 charged during unusual muscular exertion, and the subsequent effects 

 of the exertion on the general system. 



* Hoppe-Seyler, Handbuch der Physiologisch- und Pathologisch-Chemischen 

 Analyse. Berlin, 1870, p. 120. 



f Proceedings of the Koyal Society of London, vol. xvi., p. 48, and March 2, 1871. 

 j New York Medical Journal, June, 1871. 



