296 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the food, particularly in that of the young. It has been shown that if young 

 dogs are fed upon a diet poor in Ca salts, the bones fail to develop properly, 

 and a condition similar to rickets in children becomes apparent, In addition 

 to their relations to bone-formation and the fact that they form a normal con- 

 stituent of the tissues and liquids of the body, calcium salts are necessary to 

 the coagulation of blood (see p. 355), and, moreover, they seem to be connected 

 in some intimate way with the rhythmic contractility of heart-muscle, and, 

 indeed, with the normal activity of protoplasm in general, animal as well as 

 plant. Notwithstanding the special importance of calcium in the body, no 

 great amount of it seems to be normally absorbed or excreted. Voit has 

 shown that the calcium eliminated from the body is excreted mainly through 

 the intestinal walls, but that most of the Ca in the feces is the unabsorbed Ca 

 of the food. It is possible that the Ca must be present in some special com- 

 bination in order to be absorbed and utilized in the body. A point of special 

 interest in connection with the nutritive value of the inorganic salts was brought 

 out by Bunge in some analyses of the body-ash of sucking animals in compar- 

 ison with analyses of the milk and the blood of the mother. In the case of the 

 dog he obtained the following results (mineral constituents in 100 parts of ash) : 



Young Pup. Dog's Milk. Dog's Serum. 



K 2 8.5 10.7 2.4 



Na 2 O 8.2 6.1 52.1 



CaO 35.8 34.4 2.1 



MgO 1.6 1.5 0.5 



F 2 O 3 0.34 0.14 0.12 



P 2 O 5 39.8 37.5 5.9 



Cl 7.3 12.4 47.6 



The remarkable quantitative resemblance between the ash of milk and the 

 ash of the body of the young indicates that the inorganic constituents of milk 

 are especially adapted to the needs of the young ; while the equally striking 

 diiference between the ash of milk and the ash of the maternal blood seems to 

 show that the inorganic salts of milk are formed from the blood-serum not 

 simply by osmosis, but rather by some selective secretory act. These facts 

 come out most markedly in connection with the CaO and the P 2 O 5 . For 

 further details as to the history of calcium and iron in the body, consult the 

 section on Chemistry of the Body, under calcium and iron. 



I. ACCESSORY ARTICLES OP DIET; VARIATIONS OF BODY-METABOLISM 

 UNDER DIFFERENT CONDITIONS; POTENTIAL ENERGY OF FOOD; 

 DIETETICS. 



Accessory Articles of Diet. By accessory articles of diet we mean those 

 substances which are taken with food, not for the purpose of replacing tissue or 

 yielding energy, but to add to the enjoyment of eating, to stimulate the appetite, 

 to aid in digestion and absorption, or for some other subsidiary purpose. They 

 include such things as the condiments (mustard, pepper, etc.), the flavors, and 

 the stimulants (alcohol, coffee, tea, chocolate, beef-extracts). They all possess, 

 undoubtedly, a positive nutritive or digestive value beyond contributing to the 



