810 POPULAR SCIENCE MONTHLY. 



accompanied by a characteristic change of color, by a transition from 

 the pale green tint of ferrous bases to the ochery or red color of 

 ferric compounds. 



We can understand now what should happen when the ferrugi- 

 nous compound is placed in contact alternately with organic matter 

 and oxygen. In the former phase the iron will yield oxygen to the 

 organic matter; in the second phase it will take again from the 

 atmosphere the combustible which it has lost, and will be again where 

 it started. The same series of operations may be continued a second 

 time and a third time, and indefinitely, as long as the alternations of 

 contact with organic matter and exposure to atmospheric oxygen 

 are kept up, the iron simply performing the part of a broker. The 

 same result will occur if atmospheric air and organic matter are con- 

 stantly together; the consumption will continue indefinitely, and the 

 iron will perform the part of an intermediary till one of the elements 

 of the process is exhausted. 



This explanation was necessary to make clear the solution of the 

 mystery of slow or cool combustion, the existence of which has been 

 known since Lavoisier, without its mechanism being understood. 

 That illustrious student gave out the theory that animal heat and 

 the energy developed by vital action originated in the chemical reac- 

 tions of the organism, and that, on the other hand, the reactions that 

 produce heat consisted of simple combustions, slow combustions, that 

 differed only in intensity from that of the burning torch. The de- 

 velopment of chemistry has shown that this figure was too much sim- 

 plified from the reality, and that most of these phenomena, while they 

 are in the end equivalent to a combustion, differ greatly from it in 

 mechanism and mode of execution. By this we do not mean to say 

 that all the combustions are of this character, and that there do not 

 exist in the organism a large number of such as Lavoisier understood, 

 and of such as the combustions effected by the intervention of iron 

 furnish the type of. Lavoisier's successors, Liebig among them, tried 

 to find reactions conformed to this type. Their attempts were un- 

 successful, but they had the happy result of revealing, if not the 

 real function of iron in the blood, at least that of the red matter in 

 which it is fixed. 



The question of the presence of iron in the coloring matter of 

 the blood gave rise to long discussions. Vauquelin denied it. He 

 made the mistake of looking for iron in the form of a known com- 

 pound, in direct combination with the blood, while later researches 

 have shown that it is found almost exclusively in the red matter that 

 tinges the globules, in a complicated combination that escapes the 

 ordinary tests; or, according to a usual method of expression, it is 

 dissimulated. Liebig also failed to find this combination, and it was 



