504 OF SECRETION AND EXCRETION. 



The immense amount discharged upon a highly albuminous diet is worthy 

 of particular notice. The quantity of urea always increases after food, at- 

 taining its maximum usually about the 3d or 4th hour, and this would cor- 

 respond with the period when digestion and absorption being completed the 

 interstitial changes in the cells and tissues throughout the body are being 

 performed with the greatest activity. When an animal is fed on fat and 

 water exclusively, or on starch and fat, with a very small admixture of albu- 

 minous compounds, or on sugar,, the excretion of urea falls even below the 

 proportion found in absolute starvation, 1 apparently because when no food, 

 or an inadequate quantity of flesh-food, is given, the animal consumes some 

 of its own flesh in order to maintain its temperature, and thus more Nitro- 

 gen is eliminated than when fat is supplied; for this, by combining with the 

 Oxygen, keeps up the temperature, and spares the tissues of the animal. It 

 is certain that nearly the whole of the Nitrogen consumed as food is elimi- 

 nated by the urine in the form of urea. Thus in an experiment made by 

 Prof. Parkes, 2 extending over sixteen days, two men who consumed in that 

 period 313.76 grammes of nitrogen in their food, discharged by the urine in 

 the same time 303.66 and 307.257 grammes of urea respectively, the differ- 

 ence being made up by the fceces and other excretions. Every grain of urea 

 may be regarded as proceeding from the disintegration of 3 grains of Protein, 

 and represents the amount of work performed in raising 1.4 ton through one 

 foot. So that on the supposition that 501.28 grains are eliminated in the 

 day, the amount of work performed would amount to 218,786 kilogrammetres, 

 or 704 foot-tons (Haughton). Genth 3 has shown that an increase in the 

 quantity of water drank is followed by a marked increase in the quantity of 

 urea eliminated, and this especially if the water be taken, not between, but 

 at, mealtimes. Certain substances consumed with the food increase the 

 quantity of urea excreted; amongst these are Urea itself and Uric Acid, 

 common Salt (Voit), Phosphoric Acid (Bocker), Glycin, Guanin, Theobro- 

 min, Cubebs, and Cantharides. 4 On the other hand, it is diminished by 

 Digitalis, Arsenic, Turpentine, and Alcohol. 



Exertion. The influence of muscular exertion on the excretion of Urea is 

 a subject to which great attention has been directed during the last few years, 

 as being likely to afford some insight into the source of muscular energy, 

 and to show whether the force exerted by muscle is derived from the disin- 

 tegration and oxidation of its own proper substance, or whether it proceeds 

 from the oxidation of certain constituents, and especially of the hydrocar- 

 bonaceous constituents of the blood, the heat derived from which the mus- 

 cular tissue is capable of converting into mechanical force. In the former 

 case we should naturally expect that the nitrogenous products of the disin- 

 tegrated muscular tissue would appear in the urine, in the latter we should 

 anticipate an increase in the amount of carbonic acid and water eliminated 

 from the body, without material increase in the excretion of Nitrogen by the 

 urine. The facts of the case, as will be seen, are opposed to the view that 

 the tissue of the muscle is materially disintegrated during exercise, and in 

 favor of the view that the energy is derived from the oxidation of hydro- 

 carbonaceous compounds. The experiments of Dr. Ed. Smith were amongst 

 the first to show that muscular exercise was not attended with any notable 

 increase in the amount of Urea eliminated. He found that with violent labor, 

 us that of the treadwheel, there was only an increase of 19 grains daily over 

 that of light labor. On Sunday there was an increase with increase of food ; 



] Ludwig, p. 381, vol. ii. 



! Proceedings of the Royal Society, 18G7, No. 04. 



3 Untorsudi. lilx-r den Einfiiiss dcs Wnssertrink. auf den Stoffwechsel, 1856. 



4 v. Gorup-Besanez, Physiolog. Chem., p. 540, 18G2. 



