738 PHYSIOLOGY OF DIGESTION AND SECRETION. 



ferments, such as pepsin, trypsin, etc., which later were generally 

 designated as enzymes (Kiihne). The separation appeared to be 

 entirely satisfactory until Buchner (1897) showed that an unor- 

 ganized ferment, an enzyme (zymase) capable of producing alcohol 

 from sugar, may be extracted from yeast cells. Later the same 

 observer (1903) succeeded in extracting enzymes from the lactic- 

 acid-producing bacteria and the acetic-acid-producing bacteria 

 which are capable of giving the same reactions as the living bacteria. 

 These discoveries indicate clearly that there is no essential difference 

 between the activity of living and non-living ferments. The so- 

 called organized ferments probably produce their effects not by 

 virtue of their specific hfe-metabolism, but in part, at least, by the 

 manufacture within their suljstance of specific enzymes. If we can 

 accept this conclusion, then the general explanation of fermentation 

 is to be sought in the nature of the enz>Tnatic processes. Within re- 

 cent years the study of the enzjTnes has attracted especial attention. 

 The general point of view regarding their mode of action that is 

 most frequently met with to-day is that advocated especially 

 by Ostwald. He assumes, reviving an older view (Berzelius), 

 that the ferment actions are similar to those of catalysis. By 

 catalysis chemists designated a species of reaction which is brought 

 about by the mere contact or presence of certain substances, the 

 catalyzers. Thus, hydrogen and oxygen at ordinary temperatures 

 do not combine to form water, but if spongy platinum is present 

 the two gases unite readily. The platinum does not enter into the 

 reaction, at least it undergoes no change, and it is said, therefore, 

 to act by catalysis. Many similar catalytic reactions are known, 

 and the chemists have reached the important generalization that 

 in such reactions the catalyzer, platinum in the above instance, 

 simply hastens a process which would occur without it, but much 

 more slowly. A catalyzer is a substance, therefore, that alters 

 the velocity of a reaction, but does not initiate it. This idea is 

 illustrated very clearly by the catalysis of hydrogen peroxid. This 

 substance decomposes spontaneously into water and oxygen accord- 

 ing to the reaction H2O2 = H2O + 0, but the decomposition is 

 greatly hastened by the presence of a catalyzer. Thus, Bredig has 

 shown that platinum in very fine suspension, so-called colloidal 

 solution, exerts a marked accelerating influence upon this reaction; 

 one part of the colloidal platinum to 350 million parts of water 

 may still exercise a perceptible effect. The blood and aqueous ex- 

 tracts of various tissues also catalyze the hydrogen peroxid readily, 

 and this effect has been attributed to the action of an enzyme (cata- 

 lase). The view has been proposed, therefore, that the enzymes of 

 the body act Uke the catalyzers of inorganic origin: they influence 

 the velocity of certain special reactions. Such a general conception 

 as this unifies the whole subject of fermentation and holds out the 

 hope that the more precise investigations that are possible in the case 



