38 PHYSIOLOGICAL CHEMISTRY. 



After forming part of the animal solids and fluids, and taking its 

 share in the vital processes, the water is again discharged; for its 

 presence in the body, like that of all the other ingredients, is not per- 

 manent, but temporary. It makes its exit from the body by four 

 different passages, namely, as a liquid in the urine and feces, and in 

 the form of vapor by the lungs and skin. The quantity expelled in 

 each case is not uniform, but varies according to circumstances. If 

 the kidneys be unusually active, the watery ingredients of the urine 

 are increased in quantity, while the cutaneous perspiration is diminished ; 

 and the state of the atmosphere and the rapidity of respiration will 

 influence the amount of watery vapor exhaled by the lungs and skin. 

 Still there is a well-marked average relation between the activity of the 

 various organs and the quantity of their excreted fluids. It appears 

 from a comparison of the researches of Lavoisier and Seguin, Valentin, 

 and other observers, that the water discharged from the system passes 

 by these different routes nearly in the following proportions : 



By exhalation from the lungs 20 per cent. 



By the cutaneous perspiration ..... 30 u 

 By the urine and feces . . . . . . 50 " 



While only four per cent, of the water is expelled with the feces, 

 ninety-six per cent, passes out by the lungs, the skin, and the kidneys. 

 It is evident, therefore, that the main bulk of the water taken in with 

 the food does not simply pass through the alimentary canal, but enters 

 the circulation, and becomes a temporary constituent of the solid tissues. 

 As it appears in the secretions it brings with it various ingredients 

 absorbed from the glandular organs ; and when finally discharged it is 

 mingled, in the urine and feces with salts and excrementitious matters, 

 and in the cutaneous and pulmonary exhalations with animal vapors 

 and odoriferous material of various kinds. In the perspiration it 

 contains mineral sulphates and chlorides, which it leaves behind on 

 evaporation. 



2, Lime Phosphate, 2(P0 4 )Ca 3 . 



This substance exists as an ingredient in all the animal solids and 

 fluids. So far as regards its mass, it is, next to water, the most im- 

 portant of the inorganic constituents of the body, its entire quantity 

 being much greater than that of any other mineral salt. For though 

 not especially abundant in the fluids and the softer tissues, it forms 

 more than one-half the substance of the bones. It is estimated by 

 Barral that the osseous tissues constitute 6.4 per cent, of the entire 

 mass of the body ; and lime phosphate forms on the average from 57 

 to 58 per cent, of the substance of the bones. This would give, for 

 a man weighing 65 kilogrammes, or 143 pounds avoirdupois, 2400 

 grammes of calcareous phosphate in the whole body. Its proportion 

 in various tissues and fluids of the human system is as follows : 



