472 ENZYMES OF YEAST. 



tative enzyme is carried down with the precipitates produced in 

 yeast juice. 



Mention may be made in this place of the investigations 

 carried out with diluted yeast juice. WROBLEWSKI (Y ) ascertained 

 that dilution is accompanied by an unexpected extensive weaken- 

 ing of the fermentative power, whilst MACFADYEN, MORRIS and 

 ROWLAND (I.) found that the addition of an equal volume of water 

 noticeably retarded the autofermentation of the juice, and that 

 double the quantity arrested the liberation of gas almost com- 

 pletely. BUCHNER (VII.), however, in repeating these experiments 

 with greater accuracy, obtained entirely different results, no 

 perceptible decrease of fermentative power being obtained by 

 diluting the juice with a fourfold volume of 9 per cent, sugar 

 solution ; whilst it was only on dilution with 2-3 volumes of 

 water that a gradual diminution was noticeable, and even this did 

 not exceed 20-25 P er cent - of * ne total fermentative power. 

 BUCHNER (X.), moreover, was able to observe the occurrence of 

 fermentation, in certain circumstances, even when the juice had 

 been diluted twenty-fivefold. According to the recent investi- 

 gations of HARDEN and YOUNG (I.), the dilution of the juice 

 obtained from top-fermentation yeast has only a very slight 

 influence on its autofermentation. 



The fermentative enzyme suffers injury through digestive 

 enzymes. As already mentioned, the fermentative power of yeast 

 juice diminishes rapidily during storage, a result attributed to the 

 proteolytic enzymes of the juice (see chap. Ixvi.). BUCHNER and 

 RAPP (I.) have shown that when yeast juice is treated with trypsin, 

 papayotin or pancreatin, it loses its fermentative power more 

 rapidly than the check samples, either on account of the direct 

 action of the digestive enzymes, or indirectly in consequence of 

 the decomposition of the high molecular proteids that protect the 

 fermentative enzyme. 



One of the most essential conditions for the investigation of 

 cell-less fermentation is, of course, to exclude all action on the 

 part of living organisms. H. LANGE (II.) tried to ascertain how 

 far the presence of yeast cells in the crude juice affects the 

 development of fermentation phenomena, and found that even 

 when the proportion was ten times greater than the normal, it 

 was incapable of setting up fermentation with anything approach- 

 ing the same degree of vigour in concentrated solutions of sugar. 

 Similar results were obtained, in this connection, by H. WILL (XX.). 

 BUCHNER and RAPP (I.) made intentional additions of yeast cells 

 and stale juice contaminated with bacteria ; but in no case did the 

 fermentative effect surpass that of the fresh juice. It should also 

 be mentioned that according to the experiments of GERET (I.) 

 and RAPP (II.) sterile permanent yeast, and therefore also the 

 fluid contents of yeast, possess certain bactericidal properties. 



