4oo POPULAR SCIENCE MONTHLY 



testify to the multitude of chemical changes that the enzymes of the 

 animal body are capable of producing. 



Turn for a moment to the oxidation of an amino-acid such as 

 leucine, which is well known as a product of pancreatic digestion. As 

 this process is carried out in the body under the influence of specific 

 enzymes it is quite different from the ordinary conception of oxidation 

 or combustion. Instead of a complete destruction of the molecule, 

 there is first a removal of ammonia and of carbon dioxide, followed by 

 the formation of an aldehyde and an acid free from nitrogen, together 

 with acetone. The same kind of a reaction can be induced outside 

 the body by some mild form of oxidation, as with hydrogen peroxide, 

 as has recently been shown by Dakin. Here we have a series of reac- 

 tions, in which an amino-acid by successive oxidation yields a row of 

 non-nitrogenous substances such as are found in the intermediary 

 metabolism of the body, i. e., an aldehyde, an acid, and finally acetone, 

 nitrogen being removed from the molecule in the early stage of the 

 process. Such facts as these throw light upon the methods of oxida- 

 tion as they occur in the living organism, and they teach us to under- 

 stand that animal oxidation is quite different in character from the 

 old-time conception of the process. The amount or volume of oxygen 

 has no influence on the character of the change produced, but the 

 specific enzyme exercises a controlling power by means of which a 

 progressive, gradual change is induced leading to the formation of a 

 row of kindred substances of more or less physiological significance. 



In other words, the oxygen so freely drawn into the lungs at every 

 inspiration is not directly responsible for the oxidations that take place 

 in the body. Animal oxidation is a roundabout process, in which food 

 and tissue material are first through the agency of numerous enzymes 

 subjected to a variety of changes whereby easily oxidizable decomposi- 

 tion products are formed, which may eventually succumb to the in- 

 fluence of oxygen ; even here, however, enzymes of the oxidase type may 

 prove to be the controlling factor in determining whether or not 

 oxidation results. 



The " spontaneous combustion " of hay affords a striking example of the 

 activity which oxidation of the organic foodstuffs may attain when decomposi- 

 tion of the latter has previously set in. If hay is 1 stacked before it is thoroughly 

 dry, decomposition begins in the middle of the damp stack through the action 

 of organized or unorganized ferments. As all decomposition by ferments is 

 accompanied by hydration, drying is the best means of preventing it. Heat is 

 liberated by the decomposition, and proportionately with the rise in temperature 

 in the middle of the stack an ever-increasing accumulation of easily oxidizable 

 decomposition products is formed. If the hay be now disturbed so that there is 

 free access of atmospheric oxygen to the internal parts of the stack, the whole 

 blazes up and is consumed. 8 



8 Quoted from Bunge: "Text-book of Physiological and Pathological Chem- 

 istry," 2d edition, 1902, p. 252. 



