PHOSPHATE OF MAGNESIA. 423 



contained 58'7o of salts of lime, 13'7 of phosphate of magnesia, 

 and 20'4-g- of organic matters. 



The origin of the phosphate of magnesia is sufficiently obvious; 

 for this salt occurs in all parts of plants, and particularly in the 

 common varieties of grain that are used for food. From the ratio 

 in which, as we have shown, the phosphate of magnesia stands to 

 the phosphate of lime in the bones and other parts we may conclude 

 that the animal economy requires far less of this salt than of the 

 corresponding lime-salt; and this is especially illustrated by the fact 

 that in different animals it is found that the intestinal canal absorbs 

 all the phosphate of lime, but only very little phosphate of mag- 

 nesia ; for the excrements of the carnivora, as well as of the 

 herbivora, contain an excess of the latter salt. 



From these facts, Berzelius* long ago drew the conclusion that 

 the absorbents of the intestinal canal have less tendency to take up 

 phosphate of magnesia than phosphate of lime, but that rather 

 more is always absorbed by the herbivora than by the carnivora ; 

 this latter fact, however, probably depends upon the circum- 

 stance that the food of the former contains far more magnesia than 

 that of the latter class of animals. We should, however, be too 

 strictly interpreting the meaning of Berzelius if we were to sup- 

 pose that he considered the absorbents to possess any special 

 power of selecting and taking up certain substances and rejecting 

 others. The phenomenon in its whole extent is probably a mecha- 

 nical one ; the great tendency of the salts of magnesia to form 

 crystals with the salts of the alkalies, may probably in some mea- 

 sure impede their free solution and resorption. 



Berzelius found 12'9 of phosphate of magnesia, and 25'8-g- of 

 phosphate of lime in the ash of the excrements, after the use of 

 coarse bread and a little animal food. Fleitmannf found that, after 

 the use, for some days, of a diet consisting of more animal than 

 vegetable food, the excrements yielded an ash containing 10'67^ of 

 magnesia. 



The common intestinal concretions of horses consist almost en- 

 tirely of phosphate of magnesia and ammonia, with fragments of 

 straw, &c. ; in a concretion of this sort, SimonJ found 81-g- of 

 phosphate of magnesia, but no salt of lime. 



Physicians have paid much attention to the crystals of phos- 

 phate of magnesia and ammonia, which are very strikingly seen 

 in typhous stools. Although these crystals are often enough to be 



* Lehrb. d. Ch. Bd. 9, S. 345. 



t Pogg. Ann. Bd. 76, S. 383. 



t Buchner's Repertorium. Bd. 16, S. 215. 



