422 FIRST CLASS OF MINERAL CONSTITUENTS. 



it is not improbable that there are several animal substances which, 

 like sugar, exert solvent action on carbonate of lime. 



PHOSPHATE OF MAGNESIA. 



Phosphate of magnesia always occurs in such small quantity 

 that we feel scarcely justified in ascribing to it simply a mecha- 

 nical use in the animal body, and in arranging it in this class of the 

 mineral substances ; it is, however, so constantly associated with 

 the corresponding lime-salt that we feel compelled to notice it 

 in this place. Like the phosphate of lime, it is in the osseous 

 system that it is chiefly deposited. 



The bones of carnivorous animals and of man contain very 

 little phosphate of magnesia ; those of herbivorous animals rather 

 a larger quantity. Berzelius found 1'16 in a piece of human bone, 

 and 2*05^ in the bones of an ox ; Valentin found 1*943^- in a por- 

 tion of one of the ribs of a horse ; Berzelius 1'5-g- in the enamel of 

 a human tooth, and 3-g- in that of the tooth of an ox ; in human 

 dentine he found !--, and in that of the ox 2*07--. The numerous 

 analyses of von Bibra afford a general confirmation of these facts ; 

 he observed, moreover, that the teeth of the pachydermata were 

 especially rich in phosphate of magnesia. Various physiological 

 relations (age, &c.), as well as morbid conditions, augment and 

 diminish the quantity of this salt, which seems, however, to vary in 

 a direct ratio with the phosphate of lime. We shall return to this 

 subject in our remarks on "The Bones." 



That a little phosphate of magnesia occurs in all the animal 

 fluids and tissues is demonstrated by the analyses of the ash. The 

 presence of this salt is very strikingly shown by a microscopic 

 examination of the tissues of a dead body in which putrefaction has 

 actively commenced : we observe that it is everywhere studded 

 with the well-known crystals of the phosphate of ammonia and 

 magnesia. 



Phosphate of magnesia sometimes accumulates in large quan- 

 tities in certain concretions ; thus Brugnatelli* found a concretion 

 in a human ovary consisting almost entirely of this earthy salt, and 

 a similar one in the uterus, which was surrounded by a thin crust 

 of phosphate of lime. A phlebolith, examined by Schlossbergerf 



* Brugn. Giorn. T. 12, p. Ki4. 



t Ann. d, Ch. 11. 1'hann. Bd. 69, S. 254. 



