1889.] on Yeast. 579 



nitrogenons material wliicli is best calculated to promote fermenta- 

 tion. To each respectively has been added equal weights of two 

 different kinds of yeast. To one has been added yeast used in the 

 making of bread, and to the other that employed in the prodaction 

 of porter. The temperature of the fermenting fluid has been the 

 same in each case, likewise the time in uhich fermentation has been 

 progressing. The two columns of coloured liquid were filled a short 

 time previous to the commencement of the discourse, and the extent 

 to which they have been respectively depressed is a measure of the 

 amount of carbonic anhydride which has in each case been evolved 

 in the same time. You will notice that there is a marked difference 

 in the two results. 



The diagram of curves, which embodies the most typical of many 

 experiments, and in which the abscissae have been determined by 

 experiment, as shown, renders this difference clearly apparent. 



These results bring us to the heart of the question, and open up a 

 vast field of inquiry, into which for lack of time we can this evening 

 only travel a short distance. Granting that yeast is a plant — a 

 fungus — may prompt the questions as to whether it be one genus, 

 one species of a genus, or whether there be not many varieties of the 

 species which can thus give rise to fermentations so difterent in 

 character and vigour. To these questions the unrivalled researches 

 of Hansen, of Copenhagen, have given an answer which leaves no room 

 for hesitancy or doubt. 



The power of inciting alcoholic fermentation is not confined even 

 to one genus of fungi, for, although it is essentially typical of the 

 grouji known as the sprouting fungi, as opposed to the more widely 

 distributed hypLal fungi, still it is true of many of the latter, and 

 Brefeld has proved it to be the case with all the mucorini. It has 

 been asserted, moreover, that some bacteria are capable of decomj)()sing 

 sugar into alcohol and carbonic acid, thereby constituting themselves 

 alcoholic ferments. This latter question, however, is one which 

 demands further investigation. 



Before considering the morphological distinctions of the different 

 species and varieties of yeast which have been thus isolated and 

 examined, it is well to make ourselves acquainted with the nature 

 and properties of yeast, the latter being now considered as constituting 

 a generic term. [Various kinds of yeast, as employed in the arts, 

 were shown, and their morphological peculiarities, as revealed by the 

 microscope, demonstrated.] 



I am indebted to the great kindness of Dr. Hansen, which I 

 desire most cordially to acknowledge, for preparations from pure 

 cultures of all the species and varieties of yeast hitherto isolated. 

 These I am enabled to render visible to you to-night, not in the form 

 of drawings, but by means of lantern slides, which have been prepared 

 by the skilled hands of Mr. Andrew Pringle from photographs which 

 he himself took from the preparations furnished me by Dr. Hansen. 

 [Slides exhibited, and the properties of the various specimens 



