EXCRETION. 



the fact, and 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 on 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 

 mathematically 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 muscular exercise upon the 

 proportion of certain of the constituents of the urine, under 

 normal alimentation, every other modifying condition being 

 taken into account. There can be no doubt that, with ordi- 

 nary mixed diet, the elimination of urea is increased by exer- 

 cise. Fick and Wislicenus made their observations, extend- 

 ing over a period of between one and two days, under a diet 

 of non-nitrogenized matter ; and Prof. Haughton compared 

 his observations, made in July, with an average of experi- 

 ments made at different seasons, taking no account of the 

 action of the skin. It may be true that, with a purely non- 

 nitrogenous diet, exercise fails to increase the quantity of 

 urea eliminated by the kidneys, as appears from the observa- 

 tions of Fick and Wislicenus ; but further experiments are 

 necessary to settle even this point ; and recent observations 

 by Parkes show that this is not always the case. 1 



With regard to the influence of muscular exercise upon 

 the other constituents of the urine, experiments are some- 

 what contradictory. Sometimes the water is lessened, and 

 sometimes it is increased ; this probably depending upon the 

 activity of the cutaneous exhalation. Sometimes the uric 



1 See page 227, note. 



