970 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



absorption, while absorption of the phosphate may be considered as still in 

 doubt. If calcium chloride be given, a little of the calcium appears in the 

 urine, and all of the chlorine, this being due to the conversion in the intes- 

 tine of calcium chloride into calcium carbonate and sodium chloride, which 

 latter is completely absorbed. Organic salts of calcium such as the acetate are 

 absorbable, as are probably proteid combinations with calcium such as casein. 

 Milk and egg-yolk are the foods richest in calcium salts, cow's milk containing 

 more calcium to the liter than does lime-water. 1 



The excretion of calcium takes place in major part as triple phosphate from 

 the wall of the intestine, in minor part through the urine (for the latter see pp. 

 959 and 968). It is excreted during starvation, and is the principal constituent 

 of starvation feces (Voit). The secretions of the intestines, according to Fr. 

 Muller, 2 hardly contain enough calcium to account for that found in the feces, 

 so that it is probably excreted by the epithelial cells of the villus. In starva- 

 tion the source of excreted calcium is principally from the breaking down of tis- 

 sue, but partially from the metabolism of the bones. The excretion is 

 never large. On subcutaneous injection of small amounts of calcium acetate 

 in dogs, 3 the calcium excretion may be raised for several days. On venous 

 injection of 0.8 gram CaO as acetate, after one hour but 0.3 gram could be 

 found above the normal in the blood, and analysis of the liver, kidney, spleen, 

 and intestinal wall failed to reveal more than the usual minimal amounts of 

 calcium. As it is never rapidly excreted it must have been temporarily depos- 

 ited in some unknown part of the body. Bey 4 believes the large intestine to 

 be the principal organ of calcium-excretion, while F. Voit 5 attributes thi& 

 function to the small intestine. 



STRONTIUM, Sr = 87.5. 



Cremer 6 has shown, on adding strontium phosphate to almost calcium-free food of young 

 growing dogs, that the strontium line could be detected in the subsequent spectral analysis- 

 of their bones. Weiske, 7 on feeding young rabbits with food nearly free from calcium, 

 and with addition of strontium carbonate, found the ash in some of the bones to contain, 

 in the place of CaO, as high as 4.09 per cent, of SrO. In both of the above experiments 

 the skeleton remained very undeveloped in comparison with the normal, so that strontium 

 cannot be considered a physiological substitute for calcium. 



MAGNESIUM, Mg 24.3. 



This is the second in importance of the alkaline earths. It is present 

 wherever calcium is found, but in comparison with calcium it has been little 

 investigated. It occurs principally as phosphate, but is found as carbonate 

 in herbivorous urine. Of the total quantity of magnesium in the dog, Heiss 



1 Bunge : Physiologischc Chemie, 3d ed., 1894, p. 101. 



2 Zeitschrift fur Biologic, 1894, Bd. 20, p. 356. 



1 Key: Archiv fur exper. Pathologic und Pharmokologie, 1895, Bd. 35, p. 298. 



4 Key, loc. tit. 5 Zeitschrift fiir Biologic, 1893, Bd. 29. p. 325. 



6 Sitzungsberichte der Gesellschaft fiir Morphologic und Physiologic in Miinchcn, 1891, Bd. 7, 

 p. 124. 



7 Zeitschrift fiir Biologic, 1894, Bd. 31, p. 437. 



