

COMPOSITION OF THE URINE. 411 



largely by herbivorous animals, and in which the proportion of Nitro- 

 gen is as 1 : 12-14. On the other hand, whilst the proportion of Car- 

 bon in Albumen is as 1 : 1-80, it is in Kreatinine as 1 : 2-35, in Krea- 

 tine as 1 : 2-73, in Uric Acid as 1 : 9-80, in Allantoin 1 : 3-87, and in 

 Urea as 1 : 5-00. Here, again, Hippuric acid is exceptional ; for its 

 Carbon is as 1 : 1*57 of the whole, or in larger proportion than in Al- 

 bumen. We may say, then, that the characteristic components of the 

 Urinary secretion are such products of the waste of the azotized tissues, 

 as, from containing nitrogen in large proportion, are not adapted for 

 elimination, either by the respiratory process, or by the biliary excre- 

 tion. The only exception is in the case of Hippuric acid'; and the large 

 proportion of carbon and the small proportion of nitrogen contained in 

 this substance, appear due to the great* excess of non-azotized com- 

 pounds in the food of the animals voiding it. 



731. Of the compounds just enumerated, the most important, in 

 Man, is that which is named Urea. It exists in Urine in a state of 

 perfect solution ; and may be readily separated from it in the form of 

 transparent colourless crystals, which have a faint and peculiar but not 

 urinous odour. In its ultimate composition it is identical with Cyanate 

 of Ammonia, being made up of 2 Carbon, 4 Hydrogen, 2 Nitrogen, and 

 2 Oxygen, a formula much more simple than that of almost any other 

 organic substance. The amount of Urea in the Urine is liable to very 

 great variation, in accordance with the degree in which the disintegrating 

 process has been taking place in the solid fabric ; and also in confor- 

 mity with the amount of azotized matter, which has been taken in as 

 food. Supposing that the latter were so precisely adjusted to the wants 

 of the system, as to supply only that which is required for its mainte- 

 nance, we might then measure the amount of previous waste, by the 

 quantity of Urea present in the Urine. There can be no doubt as to 

 the fact, that, other things being equal, the amount of Urea is greatly 

 increased by any unusual exertion of the Muscular system ; but such 

 an increase cannot be invariably, or even usually, attributed to this 

 cause ; since it is equally certain, that any superfluity in the amount of 

 azotized matter received into the blood, must be drawn off by the uri- 

 nary excretion, and thus that an increase in the quantity of urea may 

 be occasioned by an excessive use of proteine-compounds as articles of 

 food. The average proportion of Urea, under ordinary circumstances 

 as to diet and exercise, seems to be from 20 to $5 parts in 1000 ; but 

 it may be raised to 45 parts by violent exercise, and to 53 parts by an 

 exclusively animal diet ; whilst it may fall as low as from 12 to 15 

 parts, when the diet is deficient in azotized matter. The total daily 

 excretion of Urea in adult males seems to average about 430 grains, 

 and that of females nearly 300 grains, but these averages may be 

 widely departed from, on the side either of excess or diminution, 

 according to the circumstances already noticed. It is interesting to 

 observe, that children of eight years old excrete, on the average, half 

 as much Urea as adults ; whilst, in very old persons, the quantity sinks 

 to one-third, or even less. In proportion to their relative bulks, there- 

 fore, children excrete at least two or three times the quantity of urea 

 that is set free by adults, and four or five times that which is excreted 





