430 OF NUTRITION. 



in the Horse, while a relatively larger proportion enters the urine in the 

 Cat: this is probably because the great bulk of the carbon in the food of 

 the Horse exists in those non-azotized compounds, which can be readily con- 

 verted by oxygenitiou into carbonic acid and water, and which consequently 

 yield little or nothing to the urine; whilst those products of the decomposi- 

 tion of albuminous substances which pass into the urine, though especially 

 rich in nitrogen, carry with them a certain measure of carbon into that ex- 

 cretion. In the case of man, the researches of Pettenkofer and Voit show 

 that with ordinary food 54 per cent, of the Water discharged from the body 

 is eliminated by the kidneys, 5 percent, with the fseces, and 41 per cent, with 

 the expired air. The amount of Carbon discharged per diem on mixed food 

 by the skin and lungs is about 3900 grains, of which 4 per cent, is excreted 

 by the kidneys, 6 per cent, by the bowels, and 90 per cent, by the lungs. 

 The amount of Hydrogen gas eliminated is small, and the major portion of 

 this element passes away in combination with oxygen as water. The quan- 

 titv of Nitrogen varies considerably, but with sufficient mixed diet is equal 

 to*300.6 grains daily. P.irkes 1 finds that of this, 25 grains pass off by the 

 bowels per diem, the remainder being eliminated by the urine. The propor- 

 tion of the alvine to the total excretion of nitrogen varies from 8.1 11.45 

 per cent. (Parkes) ; according to Ranke it is 8 per cent, The amount of 

 Oxygen absorbed with sufficient food is 12.845 grains, whilst during fasting 

 it is 14,793 grains. In the fasting state mor oxygen is taken up than car- 

 bonic acid is eliminated, the proportion being 106: 100; Avhen food is taken, 

 on the other hand, the proportion of oxygen absorbed to carbonic acid elim- 

 inated is as 100 : 90 ; in the latter case the carbon is derived from the-hydro- 

 carbons or carbohydrates in the food, whilst in the former it is derived from 

 the tissues, in which case a much larger amount of oxygen is required, the 

 carbohydrates containing much more oxygen. 



342. Thus, then, we see that, throughout life, a continuous interchange of 

 material takes place in the very substance of the tissues, and the new mate- 

 rial, derived from without, is being constantly laid down to replace the old 

 and effete substance, which, in the act of developing force in one form or 

 another, undergoes oxidation, and, as we shall hereafter see (chap, xi, sect. 

 3), is then taken up by the circulating current, to be removed by the excre- 

 tory organs. In the earliest periods of life, how active soever the oxidizing 

 processes may be, the power of the fabric to seize and apply the substances 

 employed as food is superior, and the results are seen in the processes of 

 growth and development. In adult life the balance is more equally pre- 

 served, and all the faculties of the body attain their highest state of efficiency. 

 But in old age, with the increasing debility of all the vegetative processes, 

 with diminished capability of absorption, diminished energy and rapidity of 

 the circulating current, with more compact and drier tissues, there comes to 

 be a gradual deficiency in the processes of nutrition, until at length the 

 body ceases to be able to nourish itself, the waste is greater than the supply, 

 and the death of extreme old age may be justly compared, in the wasting 

 oftentimes preceded by the degeneration of the tissues and the gradual 

 failure of the temperature, to death by inanition. 



.'U3. Of all the constituents of the body, none are of more complex 

 chemical composition, and undergo more numerous and varied changes, than 

 Albumen. 2 The relations which this substance bears to the living body are 



1 On the Elimination of Nitrogen from the Human Body, Croonian Lectures, 

 Lancet, vol. i, 1871. 



2 Tho formula given for it by v. Gorup-Besanez being C 216 H 162 N 27 S 3 O GS , and by 

 Theile C H8 H,, t N 17 8 2 46 - 



