424 FIRST CLASS OF MINERAL CONSTITUENTS. 



found in the faeces in other diseases, it must be granted that their 

 occurrence is by far the most frequently to be noticed in abdominal 

 typhus ; indeed, it is well known that the ulcerated patches of the 

 intestine are usually thickly studded with minute crystals of this 

 nature. 



Phosphate of magnesia is always found in the urine of man and 

 of carnivorous animals, and its presence is rendered very percep- 

 tible when the urine becomes alkaline, by the readiness with which 

 it crystallises in combination with ammonia. As we shall return to 

 this subject in the second volume, it is sufficient to observe in the 

 present place, that these crystals are always formed in normal 

 urine when alkaline fermentation commences. In serious lesions 

 of the bladder or the spinal cord, we often find whole sediments 

 consisting of these crystals. These deposits are, for the most 

 part, either devoid of colour, or of a dirty white tint. In a spe- 

 cimen of diabetic urine, I once found a glistening white sediment, 

 consisting entirely of these crystals, and not containing a trace of 

 lime. Urinary calculi, consisting of pure phosphate of magnesia, 

 are very rare, although more common than \hefusible calculi which 

 are composed of a mixture of phosphate of lime with phosphate of 

 ammonia and magnesia. 



FLUORIDE OF CALCIUM. 



It is only in very minute quantities that this body occurs in the 

 animal organism ; it is, however, so integral a part of the enamel of 

 the teeth, that we are inclined to ascribe to its presence (at least in 

 part) the polish and the extraordinary hardness of that substance. 

 The presence of small quantities of fluoride of calcium has been 

 determined with certainty in the bones of almost all animals. 

 More fluoride of calcium has been found in the skeletons of fossil 

 animals than in those of our own time ; and it is worthy of notice, 

 that human bones found at Pompeii, contain, according to Liebig,* 

 more fluoride of calcium that recent human bones. 



Berzeliusf found 2'1-g- of fluoride of calcium in the dentine and 

 3'2 in the enamel of a man's tooth, w r hile the dentine and the 

 enamel of that of an ox contained respectively 5*69- and 4-{J- of 

 this constituent. MarchandJ found 1-g- in the femur of a man 

 aged 30 years, and Heintz, 2'05-g-. 



* Organ. Ch. auf Agricultur u. Physiol. angewendet, 1840, S. 140. 



t Alt. Gehlen's Journ. 13d. 3, S. 1. 



$ Journ. f. pr. Ch. Bd. 2?,_S. 83. 



$ Ber. d. Ak. d. Wiss. z. Berlin. Febr. HUD, S. 51. 



