HEALTH AND DISEASE 



earthy bases are chiefly combined with sulphuric acid, though a portion 

 are in combination with carbon dioxide, and it is the lime carbonate in 

 minute delicate crystals that gives the cloudy appearance to the urine of 

 the horse, sometimes even when quite freshly drawn. A small quantity of 

 nitrogen is eliminated in the form of ammonia and the salts of that alkali, 

 but the proportion discharged from the system in this form, as compared 

 with the total amount of nitrogen, is only as 1 : 214. 



A few observations may be made upon each of the principal constitu- 

 ents of the urine. The first and most important of the organic constitu- 

 ents is the urea, the composition of which is CO (NH 2 ) 2 . The interest 

 attaching to this substance is that nitrogen constitutes nearly half its 



weight (46 - 6 per cent). Now nitrogen 

 does not enter into the comjDosition 

 of either the fats or the starchy or 

 saccharine components of our food, 

 whilst it constitutes about 16 per cent 

 of the various proteids, such as those 

 which form the greater part of flesh, 

 and are found in blood, milk, eggs, 

 and in the gluten of fruits and seeds 

 of the cereals and leguminous plants. 

 The quantity of nitrogen which is 

 Fig. 135.— Crystals of Urea discharged as urea rises and falls with 



the quantity of nitrogen-holding sub- 

 stances supplied in the food and absorbed in the intestines, and it thus 

 forms a measure of the amount of proteids that have been ingested. 

 Upon the average 16 grains of nitrogen correspond to 100 grains of dry 

 albumen broken up and consumed in the body. Or, expressing it in 

 another way, every grain of nitrogen in the urine corresponds to the 

 consumption of 30 grains of flesh of the animal, to the manufacture of 

 which it is supposed that all the gluten and albuminoids in the food are 

 applied, and so every grain of urea (= 0"467 N) in the urine corresponds 

 to 137 grains of disintegrated flesh of the animal. The quantity of urea 

 in the urine is not materially augmented by muscular work, which is 

 one of the facts relied upon to prove that muscular force is generated, 

 not from the disintegration and metabolism of the muscle itself, but of 

 the starchy and fatty constituents of the body. Just as in a locomotive, 

 the force expended in effecting change of place is derived, not from the 

 wear and tear of the iron framework of the machine, but from the oxy- 

 genation and combustion of the carbon of the fuel. 



The orioin of urea, it is believed, must be sought for in a substance 



