IRON 47 



increased, although they grow much more rapidly than the similarly 

 fed animals which do not receive iron. This would appear to indicate 

 that inorganic salts of iron are utilizable for certain purposes in the 

 body connected with the growth of the animals, but not for the building 

 up of hemoglobin. This conclusion, however, would be premature. 



Recent acquisitions to our knowledge of the structure of the hematin 

 moiety of the hemoglobin molecule have shown that it contains a 

 particular molecular grouping, namely, the Pyrrole Group : 



__c c 



II II 

 c c 



\/ 



N 



which there is every reason for supposing cannot be synthesized by 

 animals but must be obtained by them preformed, that is to say from 

 the tissues of plants or from the tissues of animals which acquired it 

 from plants. This pyrrole grouping is contained in small amounts in 

 the majority of proteins and it forms a very important component of 

 Chlorophyll, the green coloring-matter of plants which, as we shall see, 

 is very closely related, chemically, to hemoglobin. It is not improb- 

 able, therefore, that inorganic iron-salts added to an exclusive milk- 

 diet are not utilized for building up hemoglobin simply for the reason 

 that other component parts of the hemoglobin molecule, as essential as 

 iron itself, are either lacking altogether in the milk-diet or present 

 therein in insufficient amount to subserve the needs of the blood-form- 

 ing tissues and those of the other tissues of the body as well. We will 

 return to this question in later chapters in connection with the 

 chemistry of hemoglobin, and again in connection with the general 

 problems of growth and nutrition. 



The percentages of iron which are contained in several common 

 articles of food are enumerated in the following table: 



IRON-CONTENT OF FOODS IN PER CENT. OF EDIBLE PORTION, AFTER 



SHERMAN. 1 



It will be noted that the iron-content of spinach is very high. Spin- 

 ach is also very rich in chlorophyll, as its deep green color indicates, 

 and thus contains a large proportion of another essential constituent 



1 Chemistry of Food and Nutrition, New York, 1918. 



