VARIATIONS IN THE COMPOSITION OF THE URINE. 429 



prevailing ideas on this subject. When, for example, it has been shown that restriction 

 to a non-nitrogenous diet will immediately diminish the daily elimination of urea more 

 than one-half, it is evident that the diet must always be fully considered in experiments 

 upon the effects of exercise or of other modifying circumstances. 



There is another important point, also, which is not always taken into consideration 

 in comparative observations upon the absolute quantities of urea eliminated during exer- 

 cise and repose ; and that is the elimination of this principle by the cutaneous surface. 

 We have already seen that urea is a constant constituent of the sweat. Speck, who 

 found that exercise usually increased the elimination of excrementitious matters, noted 

 the fact that urea was not increased in the urine when the sweat was very abundant. 



A very elaborate analysis of the principal observations on this subject by Parkes 

 shows the discrepancies in the experiments of different authors and points out several of 

 the sources of error. The weight of experimental evidence formerly was decidedly in 

 favor of an increase in the elimination of urea by exercise ; and the observations opposed 

 to this view involved inaccuracies which would explain, in part at least, the contradictory 

 results obtained. Lately, however, new observations have been made, which are assumed 

 by some to show an actual diminution by exercise in the quantity of urea excreted. Fick 

 and Wislicenus, Frankland, and Haughton, have attempted to show that this is the fact, 

 and these physiologists have come to the conclusion that muscular force involves chiefly 

 the consumption of non-nitrogenous principles and the production of carbonic acid. 

 While the experiments upon this subject have been so meagre, it would be unprofitable to 

 enter into an elaborate discussion of their merits, particularly as they have not been 

 directed specially to the influence of exercise upon the composition of the urine, but to 

 the amount of muscular power developed by different kinds of food. This subject has 

 not been reduced to such an absolute certainty that we are able to calculate mathemati- 

 cally the heat-units, the digestion-coefficients, and the amount of " work " produced by 

 any given quantity of food ; and such calculations cannot, as yet, take the place of actual 

 experimental observations. What we want to know is the measurable influence of mus- 

 cular exercise upon the proportion of certain of the constituents of the urine, under nor- 

 mal alimentation, every other modifying condition being taken into account. There can 

 be no doubt that, under an ordinary mixed diet, the elimination of urea is increased by 

 exercise. Fick and Wislicenus made their observations, extending over a period of between 

 one and two days, under a diet of non-nitrogenized matter ; and Prof. Haughton com- 

 pared his observations, made in July, with an average of experiments made at different 

 seasons, taking no account of the action of the skin. It may be true that, with a purely 

 non-nitrogeneous diet, exercise fails to increase the quantity of urea eliminated by the 

 kidneys, as appears from the observations of Fick and Wislicenus ; but farther experi- 

 ments are necessary to settle even this point, and the recent observations by Parkes show 

 that this is not always the case. 



With regard to the influence of muscular exercise upon the other constituents of the 

 urine, experiments are somewhat contradictory. Sometimes the water is lessened and 

 sometimes it is increased ; this difference probably depending upon the activity of the 

 cutaneous exhalation. Sometimes the uric acid is increased and sometimes it is dimin- 

 ished. The sulphates, phosphates, and chlorides, are generally increased. 



The general result of experimental observations on the effects of exercise upon the 

 urine may be summed up in the proposition that this condition increases the activity of 

 the nutritive processes, and produces a corresponding activity in the function of disas- 

 similation, as indicated by the amount of excrementitious matters separated by the 

 kidneys. 



We have had an opportunity of settling definitely the vexed question of the influence 

 of muscular exercise upon the elimination of nitrogen. 1 In 1870, we made an exceedingly 



* FLINT, JK., On the Physiological Effects of Severe and Protracted Muscular Exercise. New York Medical 

 Journal, 1S71, vol. xiii., p. 609, et seq.; and Source of Muscular Power, New York, 1878. 



