308 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1925 



(liiction of alcoholic beverages, and has in a sense been cultivated for 

 (he purpose. This 3'east represents, as far as is loiown, one species — 

 namely, ^accliaromyces cercvisicp — altliough there are many races 

 and varieties which differ considerably in certain respects, as, for 

 instance, in the rapidity Avith which they bring about fermentation, 

 (he degree of attenuation which the}^ can effect, and the flavor of 

 the finished product. 



The "wild"' yeasts are yeasts which occur wild in nature, fre- 

 (juently having thoir habitat on the surface of ripe fruits, and often 

 linding their way into the brewery. Some of these yeasts, such as 

 (he wine yeasts, are capable of fulfilling useful functions; others 

 again are, so far as is known, Avithout effect good or bad; whilst 

 others ai'e industrially i)athogenic — that is to say, give rise to prod- 

 ucts which are un[)leasant in respect of flavor or smell or which 

 I'xhibit some other defect, such as pronounced and persistent 

 turbidity. 



The im[»ortance of these observations in connection Avith industrial 

 fermentation processes may easilj' be imagined. Prioi* to the isola- 

 tion and study of the various yeast species, and to the microscopical 

 (ontrol to wliich it naturally h'd, industrial fermentations were very 

 largely a matter of chance. Sometimes the results were good, some- 

 times they were bad, but none could say precisely why. Now all that 

 IS changed, and Avhen it is remembered that the industrialist who is 

 concerned Avith any fermentation process is threatened on .all sides 

 by intruding organisms which may have the effect of reducing his 

 yields or spoiling his products, the need for scientific control, and 

 for the constant employment of the microscope will be evident, 



I noAv propose to turn for a feAV minutes to a consideration of the 

 cytology, or, if I may be permitted the expression, the anatomy- of 

 the yeast cell. For a great many j-ears after 3 east had been subjected 

 to microscopical examination there Avas much uncertainty as to 

 whether the cell did or did not contain a true nucleus. Although the 

 existence of a nucleus is noAV Avell established, there is still some 

 doubt as to the precise nature — to say nothing of the functions — of 

 certain of the internal structures Avhich the microscope reA-eals. 

 Wager and Peniston, Guilliermond, Fuhrmann, Ilcnnebcrg, Me3'er, 

 and others have published important papers dealing Avith the cytol- 

 og}' of the yeast cell, and have shoAvn that it possesses a well-definetl 

 and complex internal structure. 



According to Wager and Peniston the main vacuole is to be re- 

 garded as the nucleus, and they consider that this is the structure 

 Avhich is cliiefly concerned in the promotion of metabolism, Avhilst 



