194 STUDIES OX FERMENTATION. 



of deposit associated with them. There is no doubt that 

 confused observations as regards these minute bodies have 

 been the cause of the error which we had to deal with in con- 

 nection with a particular mode of reproduction of low yeast, 

 as to which we have already full}^ expressed our views 

 (Chap. V. § 1, p. 146). 



Comparing Fig. 41 with Fig. 40 (p. 189), it ma}' be seen 

 that the general aspect of low yeast is distinguished, in its 

 early stages, although in no very decided manner, from that 

 of " high " yeast, by being slightly smaller and less round 

 or spherical in its cells than the latter.* These differences, 

 however, would escape an unpractised eye. 



As to the case of " high " yeast, the deposits of " low '' yeast 

 after fermentation appear as scattered, isolated cells ; we do not 

 find more than two or three per cent, of united cells. Never- 

 theless the two 3'easts present, as we shall see, quite marked 

 differences in the character of their budding and multiplication. 



On May 28th, 1875, we put a trace of pure, unicellular, 

 " low " 5'east, taken at the end of a fermentation, into a flask of 

 wort. On May 29th, sixteen hours after impregnation, the tem- 

 perature during the night having been 15° C. (59° F.), we made 

 a sketch of the yeast before its development had become apparent 

 to the naked eye. No perceptible development, that is to say, 

 no visible deposit at the bottom of the liquid and forma- 

 tion of patches of froth on the surface, took place before 

 May 30th. A mere glance at Fig. 42 wall be sufficient to enable 

 us to detect a considerable difference between it and Fig. 40, 

 which represents the multiplication of the cells of " high " 



* [We would here call the reader's attention to the following extract 

 from Dr. Graham's appreciative review of this work in "Nature," 

 January 11th, 1877. He says: " M. Pasteur seems to be in error in 

 stating (p. 190, Fr. ed.) that the bottom yeast may be distinguished by 

 being less spherical than top yeast. It is true that in London and 

 Edinburgh yeast, the cells will be found usually round; hard water, 

 however, such as that at Burton, or artificially made so, yields yeast in 

 which the cells are distinctly ovoid in appearance, resembling very closely 

 Bavarian bottom yeast." — D. C. E.] 



