THE CHEMISTRY OF DIGESTION 991 



oxide from amino-acids and their conversion into the corresponding amine. This 

 change is commonly produced by bacterial action, but may also take place normally 

 as a step in the oxidation of the carbon atoms in the carbohydrates and long chain 

 fatty acids. 



(d) Oxidation and i2e6Z^^cfion.—=-This process consists in the successive- conversion 

 of substances into CO2 and water under an evolution of energy which is much greater 

 than that derived from the changes enumerated previously. 



One of the important deductions to be derived from this tabulation 

 is that catalyzers and especially ferments, not only accelerate decompo- 

 sitions, but are also instrumental in reforming the original substance 

 from its simple end-products. This phenomenon which is known as 

 reversibility, was first shown to take place by Croft HilP in two experi- 

 ments with sucrose and invertase. An especially good example of such 

 a reversible action has been furnished by Kastle and Loevenhart.^ 

 By employing the simple ester ethyl-butyrate, they were able to prove 

 that lipase not only hydrolyzes this substance into ethyl-alcohol and 

 butyric acid, but also synthetizes these products of hydrolysis into 

 ethyl-butyrate and water. It appears, therefore, that one and the 

 same enzyme may serve not only to split a foodstuff into its simple 

 constituents, but also to reconstruct the latter into a more complex 

 substance while they traverse the lining of the intestine or enter the 

 tissues. Some investigators assert that this reversibility is something 

 more than a mere establishment of an equilibrium and conforms closely 

 to a true synthesis (Bertrand). 



It is also to be noted that ferments act best at an optimum tempera- 

 ture of 40° to 50°C. While this is true of all catalyzers, ferments seem 

 to have a more restricted sphere, low and high temperatures being 

 detrimental to them. At 60° to 80°C., they lose their power, and are 

 destroyed absolutely at 100°C. It is also apparent that the action of 

 catalyzing agents increases with their surface. An analogous process 

 is presented by the condensation of a gas upon a solid surface or by the 

 combination of hydrogen and oxygen by means of finely- subdivided 

 platinum. In addition, it has been assumed that the unusual power 

 of ferments is due to their ability of forming certain intermediate 

 products which, although they do not energize the reaction itself, 

 serve as a means of attaining the end-stage of the catalysis more 

 rapidly. As a last factor influencing ferment action might be men- 

 tioned the number of ferment-molecules involved. Thus, it has been 

 found that the degree of the change effected in a given period of time, 

 is proportional to the amount of the ferment engaged in this process, 

 and is in a measure independent of the concentration of the substra- 

 tum. It should be remembered, however, that ferments act in infin- 

 itesimally small quantities, and that an abundant supply of them is 

 rather deleterious to the reaction. The reason for this diminution in 

 the effectiveness of a ferment, when present in large amounts, is not 



1 Brit. Med. Jour., 1903, also Mathews and Glenn, Jour. Biol. Chem., ix, 1911, 

 29. 



2 Am. Jour, of Physiol., vi, 1902, 331. 



