Chemical Changes in Animal Organism. 291 



sugar, and a drop or two of gastric juice will render 

 soluble very appreciable quantities of coagulated egg- 

 white. 



Facts of this character led Moritz Traube to enunciate 

 in 1858 his theory that the chemical changes produced by 

 living organisms are brought about by certain definite 

 chemical substances contained within them, which are now 

 designated ferments or enzymes (Greek ev, in ; v/xr?, yeast). 

 Nevertheless, for a long time all attempts to obtain a pro- 

 duct from yeast which could exert the fermentative power 

 of the living organism were without result, and for a period 

 bodies capable of producing chemical change when present 

 in only relatively very small quantities were divided into 

 two classes, namely, organized and unorganized ferments. 

 Yeast, which was found to be able to ferment sugar only 

 when in a living condition, was assigned to the latter 

 class, whereas the starch-digesting product obtained by the 

 extraction by water of germinating barley, or diastase as 

 it is called, was assigned to the former. In 1897, how- 

 ever, Eduard Buchner showed that if yeast cells were 

 thoroughly disintegrated by grinding with kieselguhr and 

 sand, and the disintegrated mass was then exposed to 

 a high pressure, a juice could be obtained perfectly free 

 from yeast cells which was able to convert sugar into 

 alcohol and carbon dioxide. From this time onwards the 

 distinction between organized and unorganized ferments 

 has gradually dropped, and although certain fermentative 

 processes can still only be brought about by the intact cell, 

 this is probably due to the fact, not that the cell is living, 

 but that the action is due to two or more substances con- 

 tained in it, which are immiscible ; in other words, the 

 action takes place in a heterogeneous system, in which the 

 conditions of aggregation are disturbed when the cell is 

 destroyed. 



