102 CHEMICAL COMPONENTS OP THE HUMAN BODY. 



f . 



salt (which has been recently determined to be composed of 3 equivs. Lime + 1 

 equiv. Phosphoric acid, and not, as Berzelius supposed, 8 equivs. Lime -f 3 equivs. 

 Phosphoric acid) presents itself in the greatest abundance. In healthy bones, 

 its proportion ranges from 48 to 59 per cent. ; being greatest, as Yon Bibra has 

 shown, in those bones which are most required to possess resisting power. 1 In 

 the Dentine of teeth, its proportion rises to 66 per cent. ; and in the Enamel to 

 nearly 90 per cent. It is remarkable that, in this last situation, it should pre 1 - 

 sent an almost crystalline mode of aggregation, whilst the Enamel is the hardest 

 of all organic substances, being capable of striking fire with steel ; and it seems 

 scarcely possible to avoid tracing a connection between these two facts, more 

 especially as phosphate of lime, in certain states of crystallization, forms one of 

 the hardest of all mineral bodies. On the other hand, in bones which are un- 

 dergoing softening from any form of disease, the proportion of phosphate of lime 

 is diminished ; and an artificial softening may be induced by restricting animals 

 to food containing little or none of this salt. In regard to the mode in which 

 it is deposited there is a strong probability (as already remarked, 33) that the 

 earthy salt forms a definite chemical compound with the organic base. It is not 

 only in the skeleton, however, that phosphate of lime presents itself; for it is a 

 constituent of all the soft tissues of the body, being intimately united with the 

 organic compounds which are their essential constituents. Thus the ash of 

 Cartilage, amounting to more than 4 per cent., chiefly consists of bone-earth; 

 and well-dried Muscular fibre contains about 1 per cent, of this substance. It 

 would almost seem, indeed, to be a necessary accompaniment to the protein- 

 compounds, which are with difficulty freed from it completely ( 20, 22). As 

 might be expected, therefore, it is met with in solution in all the animal fluids ; 

 both those which contain the nutritive materials, and those which are conveying 

 out of the body the waste matters of the system. In the former, it is no doubt 

 held in solution by the protein-compounds ; thus in Milk, we find it in intimate 

 union with the casein, which has a special solvent power for bone-earth ; and in 

 Blood it is in like manner united with the albumen, and, in a less degree, with 

 the fibrin. All fluids into which these substances pass, even in a state of in- 

 cipient metamorphosis as the lymph of the lymphatics, the serous fluid which 

 permeates the lacunae of the tissues, the salivary, gastric, and pancreatic secre- 

 tions, &c. contain phosphate of lime as their accompaniment. On the other 

 hand, it forms a considerable proportion of the inorganic constituents of the 

 urine ; and there its condition is entirely different, as it is completely dissociated 

 from organic matter. Its solubility in that fluid seems due to the fact that, 

 although entirely insoluble in water, a small quantity of this salt is taken up by 

 solutions of chloride of sodium or of hydrochlorate of ammonia, or by fluids 

 charged with carbonic acid. And it is further remarkable, that lactic acid has 

 a special solvent power for phosphate of lime; as much as 68 parts of this salt 

 being dissolved by 100 parts of the anhydrous acid. It is probable, as pointed 

 out by Lehmann, that phosphate of lime may be formed within the body, by the 

 union of phosphoric acid set free from the alkaline phosphates, or generated by 

 the oxidation of phosphorus, with carbonate of lime contained in the food or 

 water consumed; but there cannot be a doubt that the greater part of what is 

 contained in the body, is introduced there ready formed. Of its abundance in 

 the aliment of carnivorpus animals, there is no need to say more ; and it is 

 present to a large extent in all the most nutritious articles of vegetable food, 

 especially in the corn-grains. 



77. Although the phosphate of lime is the principal solidifying ingredient 

 of the Bones and Teeth of the higher animals, yet they also contain a considera- 



1 See his "Chemische Untersuchungen xiber die Knocken und Ziihne des Menschen, 

 und der Wirbelthiere," Schweinfurt, 1844. 



