104 CHEMICAL COMPONENTS OP THE HUMAN BODY. 



than it does in animal flesh ; and as no more seems to be taken up than the sys- 

 tem requires, the residue is carried off in the feces, of whose ash from 10 to 

 13 per cent, has been found to consist of phosphate of magnesia when a mixed 

 diet was employed. It seems to be from the superfluity of this salt in their 

 food, that the tendency to intestinal concretions arises in many herbivorous ani- 

 mals ; those which are common in the horse, for example, consisting almost 

 entirely of the triple phosphate, with fragments of straw, &c. The proportion 

 of this salt which is absorbed, and which is embodied in the various tissues, 

 seems normally to enter the urine when set free by their disintegration, and to 

 be thus carried out of the body, at a rate corresponding to that of its introduc- 

 tion. If, however, free ammonia should be generated, either by decomposition 

 of the urine, or by a state of incipient putrescence of the solids or fluids of the 

 body, the triple phosphate is produced ; and thus it is that it is often found in 

 considerable amount in the urine, and that it presents itself in the fecal evacua- 

 tions in cases of typhoid fever. That it is a real excretion in the latter case, is 

 sufficiently obvious from the fact that it cannot have been furnished by the 

 food ; and it is interesting to observe that its crystals are found thickly studding 

 the ulcerated patches of intestinal glandulse, which are probably the seat of their 

 elimination. There is no reason to think that the function of phosphate of mag- 

 nesia in the system is less mechanical than that of carbonate of lime. 



79. A minute proportion of Fluoride of Calcium has been so constantly 

 found in the bones, that it may be considered as one of their ordinary compo- 

 nents ; how far, however, its presence is to be regarded as essential, or how far 

 it depends upon the combination of this with other calcareous salts contained in 

 the food, has not yet been determined. That it is specially attracted by osseous 

 tissue, even when this is no longer alive, appears from the fact that fossil bones 

 are often found to contain it in extraordinary amount, no less than 15 or 16 per 

 cent, being occasionally discovered in them ; and this can scarcely have been 

 derived from any other source than a percolation of water charged with fluoride 

 of calcium through the strata in which the bones were imbedded. It would 

 seem, moreover, that the teeth, and especially the enamel, contain a much larger 

 proportion of this substance than does any other living texture ; thus Berzelius 

 found 2.1 per cent, of fluoride of calcium in the dentine, and 3.2 per cent, in 

 the enamel, of a human tooth. It is obvious that this compound must be de- 

 rived from the solid or liquid aliment introduced into the system, and must be 

 absorbed into the blood ; and there is experimental proof that such is the case. 

 Fluoride of calcium may be detected in many mineral waters, and is soluble, 

 according to the experiments of Dr. G. Wilson, 1 in about 28,000 times its weight 

 of water; and it is contained in the ashes of plants growing on micaceous soils. 

 The same experimenter appears clearly to have determined its presence in Blood 

 and in Milk, although he has not made a quantitative appreciation of it ; and 

 we may fairly expect that it might be detected in the Urine, if a sufficiently 

 large amount were examined, this being the channel by which it would proba- 

 bly find its way out of the body. 2 



1 Reports of British Association for 1850, pp. 67, 68. 



2 It is right here to mention that, although the presence of fluoride of calcium in the 

 animal body has been very generally admitted, a doubt has been thrown upon the validity 

 of the proofs usually relied on. Dr. G. 0. Rees states ("Guy's Hospital Reports," No. 

 ix.) that he could not succeed in unequivocally detecting this salt in bone-ash, although as 

 little as 0.3 gr. added to 100 grains of bone-ash produced unequivocal corrosion of glass ; and 

 he is disposed to attribute the very different results obtained by other Chemists, to the 

 power of phosphoric acid to corrode glass of inferior quality. It may be, however, that 

 the presence of this salt is purely accidental, depending upon an impregnation of the 

 waters of the neighborhood, and upon its reception into plants growing under circum- 

 stances in which it is abundantly supplied. If this be the case, it might be met with in 

 considerable amount in some bones, and be entirely wanting in others. 



