808 POPULAR SCIENCE MONTHLY. 



investigation, where accuracy is necessary down to the infinitesimal 

 fraction. The balances of the biologists must weigh the thousandth 

 of a milligramme, as their microscopes measure the thousandth of a 

 millimetre. 



The great part performed by iron in organisms, what we may 

 call its biological function, appertains to the chemical property it 

 possesses of favoring combustion, of being an agent for promoting 

 the oxidation of organic matters. 



The chemistry of living bodies differs from that of the laboratory 

 in a feature that is peculiar to it — that instead of performing its re- 

 actions directly it uses special agents. It employs intermediaries 

 which, while they are not entirely unknown to mineral chemistry, 

 yet rarely intervene in it. If it is desired, for example, to add a 

 molecule of water to starch to form sugar, the chemist would do it 

 by heating the starch with acidulated water. The organism, which 

 is performing this process all the time, or after every meal, does it in 

 a different way, without special heating and without the acid. A 

 soluble ferment, a diastase or enzyme, serves as the oxidizing agent 

 to produce the same result. Looking at the beginning and the end, 

 the two operations are the same. The special agent gives up none of 

 its substance. It withdraws after having accomplished its work, and 

 not a trace of it is left. Here, in the mechanism of the action of these 

 soluble ferments, resides the mystery, still complete, of vital chem- 

 istry. It may be conceived that these agents, which leave none of 

 their substance behind their operations, which suffer no loss, do riot 

 have to be represented in considerable quantities, however great 

 the need of them may be. They only require time to do their work. 

 The most remarkable characteristic of the soluble ferments lies, in 

 fact, here, in the magnitude of the action as contrasted with in- 

 finitesimal proportion of the agent, and the necessity of having time 

 for the accomplishment of the operation. 



Iron behaves in precisely the same way in the combustion of 

 organic substances. These substances are incapable at ordinary tem- 

 peratures of fixing oxygen directly, and will not burn till they are 

 raised to a high temperature; but in the presence of iron they are 

 capable of burning without extreme heat, and undergo slow com- 

 bustion. And as iron gives up none of its substance in the operation, 

 and acts, as a simple intermediary, only to draw oxygen from the 

 inexhaustible atmosphere and present it to the organic substance, we 

 see that it need not be abundant to perform its office, provided it 

 have time enough. This action resembles that of the soluble fer- 

 ments in that there is no mystery about it, and its innermost mechan- 

 ism is perfectly known. 



Iron readily combines with oxygen — too readily, we might say, 



