INORGANIC CELL-CONSTITUENTS. 133 



to fulfill. This seems indicated by the fact that the nervous tissue in 

 solutions of alkaline phosphates may preserve its irritability much 

 longer than when in contact with any other fluid. In the tissues the 

 phosphates of the alkalies occur as acid salts ; it therefore would seem 

 that tissues in their growth require the presence of free phosphoric acid; 

 In the case of the blood, on the other hand, an alkaline reaction is 

 essential for its vital phenomena, and it appears that, provided the 

 alkaline reaction is preserved, the salt to which this alkalinity is due is 

 of minor importance. Thus, in the carnivorous animals the reaction is 

 attributable to the excess of alkaline phosphate, in the herbivorous 

 animals to the carbonates. In omnivorous animals the preponderance 

 of these different salts varies according to the character of their diet. 



8. CALCIUM PHOSPHATE (2(PO 4 )Ca 8 , 2(P0 4 )CaH 4 ). This salt is 

 present, without exception, in all tissues and fluids of the animal body ; 

 in bones and teeth nearly two thirds of their weight is due to the 

 calcium phosphate present. Of all the inorganic constituents of the 

 body, with the exception of water, it is the most abundant. In most of 

 the pathological ossifications and concretions calcium phosphate consti- 

 tutes the major portion. Thus, nearly all the urinary calculi in the ox 

 are formed by calcium phosphate, and it is also a constituent of the 

 mulberry calculus of man. So, also, calculi which develop around some 

 foreign nucleus are largely calcium phosphate. Calcium phosphate also 

 forms the greater part of the ash of albuminous bodies, with, as far as is 

 3'et known, the single exception of elastin. It is present in the tissues 

 of the human body in the following proportions : 



QUANTITY OP CALCIUM PHOSPHATE IN 1000 PARTS IN THE 



Enamel of teeth, . . . . . . . . 885. 



Dentine, ' . 643. 



Bones, .......... 576. 



Cartilage, . . .40. 



Milk, ' .- ' . . . . 2.72 



Blood, -< .... 0.30 



Bile, . . . 0.92 



Urine, 0.75 



The greater part of calcium phosphate in the organism is deposited 

 in the form of a solid salt in the bones and teeth, in the form of the 

 tricalcium orthophosphate (2(P0 4 )Ca s ). It is also in the same form 

 present in nails, hair, and hoofs. When it is found in solution, as is the 

 case with all of the animal fluids, it being by itself perfectly insoluble in 

 water, its presence is only to be explained as chemically united with 

 albuminoids, although possibly it may be in minute amount in solution 

 in fluids which contain sodium chloride or free carbon dioxide. In the 

 urine of carnivora and omnivora calcium phosphate is present as an acid 

 salt (2(P0 4 )Ca"H 4 ), which is in itself soluble in water. In the alkaline 



