356 AN AMERICAN TEXT-BOOK OF J'HYSIOLOGY. 



In this way the normal proportion of NaCl in tli£ tissues and the body-fluids 

 is lowered and a craving for the Bait is produced. Bunge states that it has been 

 shown among men that vegetarians habitually consume more salt than those 

 who are accustomed to eat meats. The salts of calcium and of iron have also 

 a special importance that needs a word of reference. The particular import- 

 ance of the iron salts lies in their relation to haemoglobin. The continual 

 formation of new red blood-corpuscles in the body requires a supply of iron 

 Baits for the synthesis of the haemoglobin, and, although there is a probability 

 (see p. 323) that the iron compound of the disintegrating corpuscles is again 

 used in part for this purpose, we must suppose that the body requires addi- 

 tional iron in the food from time to time to take the place of that which is 

 undoubtedly lost in the excretions. It has been shown that iron is contained 

 in animal and vegetable foods in the form of an organic compound, and the 

 evidence at hand goes to show that only when it is so combined can the iron 

 be absorbed readily and utilized in the body, while the efficacy of the inor- 

 ganic salts of iron as furnishing directly a material for the production of haemo- 

 globin is, to say the least, open to doubt. Bunge isolated from the yolk of 

 eggs an iron-containing nuclei n which he calls hcematogen, because in the 

 developing lien's e<i^ it is the only source from which the iron required 

 for the production of haemoglobin can be obtained. It is possible that sim- 

 ilar compounds occur in other articles of food. Most of the iron taken with 

 food, however, including that present in the haemoglobin of meats, passes 

 out in the feces unabsorbed. It is probable that there is an actual excre- 

 tion of iron from the body, and, so far as known, this excretion is effected 

 in small part through the urine and bile, but mainly through the walls of the 

 intestine, the iron being eliminated finally in the feces. The large proportion 

 of calcium Baits found in the skeleton implies a special need of these salts in 

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

 dogs are i'ed upon a diet p >or 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. 57), 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 bas 

 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 (a 

 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 bv Bunge in some analyses of the body-ash of sucking animals in com- 

 parison with analyses of the milk and the blood of the mother. In the 



