EXCHANGE OF MATERIAL. 453 



splitting products, and carnivora can therefore be kept alive for a 

 longer time. 



Lack of earthy phosphates. With the exception of the impor- 

 tance of the alkaline earths as carbonates and principally as phos- 

 phates in the physical composition of certain structures, such as 

 the bones and teeth, their physiological importance is nearly un- 

 known. The action which an insufficient supply of alkali-earths 

 with the food causes is connected with the interesting question as 

 to the eifect of this lack upon the bony structure. This action, as 

 well as the various results obtained by experiments on young and 

 old animals, has already been spoken of in Chap. VIII, to which we 

 refer the reader. 



Lack of iron. As iron is an integral constituent of haemoglobin, 

 indispensable for the introduction of oxygen, so also it is an indis- 

 pensable constituent of the food. In iron starvation iron is con- 

 tinually eliminated, even though in diminished amounts (HAM- 

 BUBGER, DIETL, v. HossLiN). From the observations of v. 

 HOSSLIN on dogs it also seems that an inadequate supply of iron 

 with the food causes an insufficient formation of haemoglobin. A 

 special result of the lack of iron is chlorosis, which the physician 

 has often to contend with and whose origin is not really a lack of 

 iron in the food, but more likely an incomplete absorption of the 

 foods containing iron (BuNGE). The iron-salts seem not to be ab- 

 sorbed at all in the intestinal canal, or only to a very small extent, 

 so that it is questionable whether their absorption has any men- 

 tionable importance. It seems more probable that the absorption 

 of iron from the food takes place in the form of protein bodies 

 (nucleoalbumin) containing iron (BUNGE); and the importance of 

 the iron-salts in preventing the lack of haemoglobin consists chiefly, 

 according to BTOGE, in that these salts counteract the decomposi- 

 tion in the intestines of the protein bodies containing iron, which 

 split off iron as iron sulphide. 



In the absence of proteid bodies in the food the organism must 

 nourish itself by its own proteid substances, and on such nutrition 

 it must earlier or later succumb. By the exclusive administration 

 of fat and carbohydrates the consumption of proteids in these cases 

 is reduced, for by an exclusive fat and carbohydrate diet the 

 metabolism of proteids may indeed be smaller than in complete 



