74 PROXIMATE PRINCIPLES OF THE FIRST CLASS. 



It is discharged with the urine, mucus, cutaneous perspiration, 

 &c., in solution in the water of these fluids. According to the esti- 

 mates of M. Barral. 1 a small quantity of chloride of sodium dis- 

 appears in the body; since he finds by accurate comparison that all 

 the salt introduced with the food is not to be found in the excreted 

 fluids, but that about one-fifth of it remains unaccounted for. This 

 portion is supposed to undergo a double decomposition in the blood 

 with phosphate of potassa, forming chloride of potassium and phos- 

 phate of soda. By far the greater part of the chloride of sodium, 

 however, escapes under its own form with the secretions. 



3. CHLORIDE OF POTASSIUM. This substance is found in the 

 muscles, the blood, the milk, the urine, and various other fluids 

 and tissues of the body. It is not so universally present as chlo- 

 ride of sodium, and not so important as a proximate principle. 

 In some parts of the body it is more abundant than the latter salt, 

 in others less so. Thus, in the blood there is more chloride of 

 sodium than chloride of potasssium, but in the muscles there is more 

 chloride of potassium than chloride of sodium. This substance is 

 always in a fluid form, by its ready solubility in water, and is easily 

 separated by lixiviation. It is introduced mostly with the food, but 

 is probably formed partly in the interior of the body from chloride 

 of sodium by double decomposition, as already mentioned. It is 

 discharged with the mucus, the saliva, and the urine. 



4. PHOSPHATE OF LIME. This is perhaps the most important 

 of the mineral ingredients of the body next to chloride of sodium. 

 It is met with universally, in every tissue and every fluid. Its 

 quantity, however, varies very much in different parts, as will be 

 seen by the following list : - 



QUANTITY OF PHOSPHATE OF LIME IN 1,000 PARTS IN THE 

 Enamel of the teeth . . 885 Muscles . . . .2.5 



Dentine . . . .643 Blood . . . .0.3 



Bones .... 550 Gastric juice . . .0.4 



Cartilages ... 40 



It occurs also under different physical conditions. In the bones, 

 teeth, and cartilages it is solid, and gives to these tissues the resist- 

 ance and solidity which are characteristic of them. The calcareous 

 salt is not, however, in these instances, simply deposited mechani- 

 cally in the substance of the bone or cartilage as a granular powder, 



1 In Robin and Verdeil, op. cit., vol. ii. 193. 



