82 POPULAR SCIENCE MONTHLY 



unaltered itself, accelerates a chemical reaction, otherwise going on very 

 slowly. To elucidate with an example: fat is a chemical union of 

 two compounds, one of which is called a fatty acid, and the other an 

 alcohol. Fat, in the absence of a fat splitting enzyme, yields very 

 small quantities of these two substances in the course of a long time. 

 But, in the presence of a proper enzyme the fat yields considerable 

 quantities of fatty acid and alcohol in a comparatively short time. The 

 rapidity of the splitting is directly proportional to the amount of the 

 enzyme added. A small amount of the enzyme will decompose just 

 as much of the fat as a large quantity will, but a longer period of time 

 is required. A quantity of the enzyme may be used over and over 

 again for splitting any amount of fat, unless it is destroyed by bacteria, 

 heat, chemicals, or some other deleterious agent. 



When fat and an enzyme are placed in a test tube together, not 

 all the fat is changed into its component parts. The reaction proceeds 

 until more than half the fat is decomposed. Then there is a reversal 

 of the chemical reaction. Fat is reformed from the fatty acid and 

 alcohol; the splitting process proceeds very slowly if at all. The fat 

 formation goes on as the predominant process in the tube until an 

 excess of fat is formed, when a reversal again occurs, and fat decom- 

 position becomes the chief reaction in the test tube. The alternate 

 breaking down and building up goes on indefinitely, like the swinging 

 back and forth of a pendulum. The sweep of the pendulum when 

 first started may be broad, but if allowed to swing uninterruptedly, 

 there is a gradual diminution of the distance traversed until the pendu- 

 lum eventually comes to a standstill. Thus it is with the chemical 

 reaction. This power of an enzyme to carry a chemical reaction in 

 either direction is spoken of as the reversibility of enzymes. This has 

 not been demonstrated to be true of all these bodies, but the physi- 

 ologist delights in the speculation that it is; and many are the prob- 

 lems planned to demonstrate this characteristic in this or that enzyme. 



Enzymes have important functions to perform in both animal and 

 plant economy. Practically all of the chemical reactions, normally 

 occurring in life processes, are believed to be aided by ferments. The 

 distribution of these bodies in an organism is general. In man they 

 are found, not only in the alimentary canal, but in the blood and 

 lymph and presumably every cell of the body. The ferments of the 

 alimentary canal are there for the purpose of splitting the food stuffs 

 into their components, which are more readily absorbable than the 

 original materials. Those of the liquids and cells of the body reform 

 and build up the food elements into the vital tissues or protoplasm of 

 the organism. 



Another process in which enzymes play an omnipotent part is that 

 of respiration. The oxidation of the protoplasmic constituents, from 



