INORGANIC SUBSTANCES. 41 



constituents of the frame ; comparatively inactive in the process of 

 internal metamorphosis, and serving for the most part as a physical 

 ingredient of the solid tissues. 



3. Lime Carbonate, C0 3 Ca. 



Lime carbonate is found in the bones, the teeth, the blood, the 

 lymph and chyle, the saliva, and sometimes in the urine. In all these 

 situations it is in much smaller proportion than the calcareous phosphate 

 with which it is associated. In the bones, however, it is next in im- 

 portance to the lime phosphate, being on the average one-seventh as 

 abundant as that salt, and much more so than any of the remaining 

 mineral ingredients. In the animal fluids, its solubility is accounted for 

 by the presence of the alkaline chlorides or by that of free carbonic acid. 



4. Magnesium Phosphate, 2(P0 4 )M-- . 



Magnesium phosphate was formerly associated with the corresponding 

 lime salt, under the name of the earthy phosphates, owing to certain 

 resemblances in their chemical relations. Like the lime phosphate, 

 which it everywhere accompanies, though for the most part in smaller 

 quantity, it is present in all the tissues and fluids of the body. Thus 

 in the bones the lime phosphate is in the proportion of 576 parts per 

 thousand, while the magnesium phosphate forms only 12.5 parts. In 

 the blood, the calcareous salt amounts to 0.30 part per thousand, the 

 magnesium salt to 0.22 part; and in the milk there are 2.72 parts of 

 lime phosphate to 0.53 part of magnesium phosphate. On the other 

 hand, the salts of magnesium have been found in larger quantity than 

 those of lime in the muscles, and nearly twice as abundant in the sub- 

 stance of the brain. 



The magnesium phosphate is discharged, by the urine, in the average 

 daily quantity of 0.6 gramme. The amount of both the earthy phos- 

 phates together is accordingly about 1 gramme per day ; the magnesian 

 salt being rather the more abundant of the two. 



Both the magnesium phosphate and carbonate, of which latter salt 

 traces occur in the blood, appear to have similar physiological relations 

 with the corresponding salts of lime, and present the same features in 

 their union with the tissues and their solubility in the animal fluids. 



5. Sodium Chloride, NaCl. 



This is undoubtedly the most important of the mineral constituents 

 of the body, as regards its general distribution and its active part 

 in the phenomena of nutrition. It is the most abundant of all, next 

 to lime phosphate, and is present in all the animal tissues and fluids. 

 Its entire quantity in the human body is estimated by Dr. Lankester 

 at 110 grammes, or nearly one-quarter of a pound avoirdupois. In 

 the blood it is nearly as abundant as all the other mineral ingredients 

 together. Its proportion in various parts of the body is as follows : 



