METABOLISM 181 



etc. Ultimately it takes the form of phosphoric acid and is 

 excreted in the feces or urine (199), but whether any inter- 

 mediate compounds are formed is not known. 



Other elements 



While the other so-called ash ingredients are no less impor- 

 tant than the two just considered, little is known regarding their 

 katabolism in the ordinary sense, i.e., of the chemical changes 

 which they undergo in the body. That they may exist in 

 feeding stuffs in organic as well as in inorganic forms is probable. 

 That they enter into organic combination in the animal body is 

 likewise to be assumed but is positively known in only a few 

 instances like that of the iron of the haemoglobin and the 

 iodin of the thyroid glands. 



259. Sodium and potassium. Both sodium and potassium 

 are contained in the ordinary foods and feeding stuffs and in 

 addition man and farm animals consume not inconsiderable 

 amounts of common salt, although it appears probable that this 

 serves to a considerable extent as a condiment and that the 

 amount actually necessary is less than is often supposed. Bab- 

 cock, e.g., was able to keep cows for over a year without access 

 to salt, except that contained in their feed, without any obvious 

 ill consequences. 



Both potassium and sodium, as well as the chlorin com- 

 bined with the latter in the form of salt, are excreted in the 

 urine. 



260. Calcium and magnesium. These elements, calcium in 

 particular, are especially important in their relations to the 

 growth and maintenance of the skeleton, but they are not lacking 

 in the soft tissues also, where they perform important functions. 

 Of their intermediary metabolism little is known. As noted 

 in Chapter IV (199), the normal path of excretion of calcium, 

 and to some extent of magnesium, is through the lower in- 

 testine, so that the apparent digestibility of these elements is 

 no measure of the amount actually resorbed and utilized in the 

 body processes. 



261. Iron. A long controversy has been carried on over 

 the question whether inorganic iron may be resorbed and if so 

 whether it can be utilized for the synthesis of the haemoglobins 



