AND ITS RELATION TO ANIMAL LIFE 5 



evidence further on, is that iron is the means of 

 fixing the ammonia of the air in the soil to 

 form nitrates. In any case, I am sure there is 

 a fixed law by which the ammonia of the air 

 is fixed in the soil to form nitrates, just as 

 chlorophyll is the medium by which carbon 

 dioxide is fixed in the plant. 



This is important, as the loss of carbon and 

 nitrogen can only be replaced by the use of 

 organic food substances, and cannot be supplied 

 from the air as oxygen can with the assistance of 

 a normal haemoglobin. 



It is of the utmost importance that the loss 

 of carbon and nitrogen should be made good, 

 where they are wanting in chlorotic food, seeing 

 that carbon enters into the composition of all 

 the organic substances such as the carbohy- 

 drates, hydrocarbons, proteids, etc. (Encyclo- 

 paedia Britannica, vol. xix. p. 48). 



We see, then, that chlorotic food does not 

 imply simply a deficiency in iron, but also a 

 deficiency in carbon, which means that chlorotic 

 food is wanting in sugars, fats, proteids, etc., 

 and as the animal can only take in carbon by 

 means of food substances, it also means that 



