1 8 PHYSIOLOGICAL CHEMISTRY. 



less in respiration, but the presence of others is an element of 

 the greatest danger, because of the disturbances they occasion 

 when taken into the body. 



MINERAL SUBSTANCES REQUIRED. 



Salts. The table some pages back gives the percentage 

 amount of the different elements which make up the human 

 body, some being united in organic and the others in inorganic 

 compounds. Aside from water the most abundant and im- 

 portant of the inorganic materials are the phosphates and 

 carbonates of the alkali-earth metals found in the bones, the 

 alkali chlorides and the alkali carbonates. The solid mineral 

 matter or ash of the adult body amounts in the mean to about 

 5 per cent; not far from four-fifths of this content comes 

 from the skeleton, while about one-tenth of it is derived from 

 the muscles. The proportion of ash in the different tissues, 

 taken in the moist condition, is approximately as follows : 



Per Cent. Per Cent. 



Bones 33 Pancreas, brain i.o 



Cartilage 2 Lung, heart 0.95 



Liver and spleen 1.5 Blood 0.93 



Muscles 1.3 Skin 0.75 



Kidney 1.2 Milk 0.70 



Leaving traces out of consideration, it appears that the body 

 contains four metallic elements, calcium, sodium, potassium 

 and magnesium, which exist in combination with four acids, 

 viz., phosphoric, hydrochloric, carbonic and sulphuric. Of 

 all these compounds the calcium phosphate of the bones is 

 the most abundant. 



Phosphates. The phosphates of the body are salts of the 

 common or orthophosphoric acid, H 3 PO 4 . The three kinds 

 of salts possible here are: 



Primary phosphates, MEUPCX, 

 Secondary phosphates, MzHPCX, 

 Tertiary phosphates, M 3 P(X 



