50 INORGANIC FOODSTUFFS 



Silicon is a constant constituent of hair and feathers, no less than 

 40 per cent, of the ash of hair consisting of SiO 2 . This is doubt- 

 less derived from silicates in the vegetable portion of our diet, 

 silicon playing an important part in communicating rigidity to many 

 plant-tissues. According to Drechsel the silicon in feathers exists 

 therein in a state of organic combination, as the silicate of a hydro- 

 aromatic alcohol closely related to cholesterol. 



Phosphorus is, of course, an element of prime importance in the 

 life-economy, in the form of the phosphoric acid radical in phospho- 

 proteins such as casein and in the form of complex substituted 

 phosphoric acids, as Nucleic Acid and the glycero-phosphoric acid 

 radical of the phosphorus-containing fats or phospholipins. This 

 phosphorus is derived from the phosphates, phosphoproteins, nucleins 

 and phospholipins in the diet. There is some room for question 

 whether animal tissues utilize the inorganic phosphates in the diet 

 for the building up of the nucleins and phospholipins. A fact which 

 seems to indicate that animals do not depend upon inorganic phosphates 

 for the production of these substances is that mice will grow normally 

 and reproduce on a diet containing a high proportion of aluminum 

 hydrate, although this results in the formation of the insoluble alumi- 

 num phosphate from any inorganic phosphates which may be present 

 in the alimentary canal, and its elimination, without absorption in the 

 feces. 



Sulphur also plays an exceedingly important role, but in the form of 

 the complex amino-acid cystine, which is a decomposition-product 

 of many proteins, rather than in the form of free sulphates or sulphides. 



Iodine is a normal constituent of the Thyroid and plays an essential 

 part in the important functions of this gland. We will consider 

 the nature of the organic combination in which it occurs and its 

 significance in the bodily economy in a later chapter. It has been 

 repeatedly stated that iodine is found in other tissues of the body, 

 notably in the pituitary gland, but more recent analyses have shown 

 that in the absence of iodide-medication, iodine is not found in normal 

 animal tissues other than the thyroid. Iodine is an important con- 

 stituent of seaweed, from the ash of which a quantity of the iodine of 

 commerce is derived. The relatively high concentration of iodine in the 

 tissues of these marine plants is of especial interest because the iodine 

 content of sea-water is exceedingly low. This constitutes therefore an 

 interesting case of the Selective Absorption by living tissues to which 

 reference was made in connection with the proportion of sodium to 

 potassium in the blood and tissues of animals. 



THE COMPLEXITY OF OUR DIETARY REQUIREMENTS. 



It is to be hoped that the recital of the above category of the inorganic 

 constituents of our body, present, several of them, in the most incon- 

 siderable traces, will have the effect of making the reader pause ere he 



