226 THE ORGANISMS IN YEAST. 



small amounts of other products, as Glycerine and Succinic Acid, 

 and the removal of a small proportion of the nitrogenous consti- 

 tuents, but the exact manner in which these changes are brought 

 about is yet to be satisfactorily ascertained. 



Of the other organisms which are present in commercial 

 Yeast, the most common beyond doubt is the Bacterium, which 

 sets up the lactic change, the Bacterium lactis of Lister, by whom 

 it is described in the Quart. Journ. Micro. Science., as " being 

 somewhat peculiar in the form of its segments, which are oval, and 

 not so rod-like as Bacteria generally " ; whilst Dr. C. Graham, in 

 his Cantor lectures of 1874, describes them as "little organisms of 

 the shape of a figure 8, two round circles together " ; and Pasteur 

 says, " Small articulations, slightly strangled in the middle, gener- 

 ally isolated, more rarely joined in chains of two and three." I 

 have been particular in giving these descriptions, as these cells are 

 often somewhat difficult of recognition. They are shown in the 

 Plate at No. 8, as seen under a 1 — 10 in. objective; but I am 

 afraid the drawing includes some other Bacteria besides the B. 

 lactis. There is no reason to doubt that this organism, in common 

 with most others of the kind, assimilates its nutriment in a manner 

 similar to the cells of Torula cerevisice, but it is devoid, so far as 

 my experience goes, of any appearance of the internal structure 

 (so to speak) which is visible in the latter, and it is so much 

 smaller in size as to be readily separated from it by means of 

 filter-paper. It is in the strict sense a fission-cell, multiplying, 

 according to Professor Lister, " by fissiparous generation, the lines 

 of segmentation being transverse to the longitudinal axis of the 

 organism," =:- and when observed, it is generally in some stage of 

 division. It is not a common organism in the ordinary atmo- 

 sphere, but when once present in a favourable soil, developes with 

 great vigour, to the hindrance of any other weaker species. It is 

 to be found in milk when souring, and in malt infusions, especially 

 developing in the latter when retained at a slightly warm tempera- 

 ture, and brings about in both, the resolution of the saccharine 

 matter into lactic acid. Even a good Yeast is scarcely ever seen 

 altogether free from this organism. 



* " 



Quart. Journ. Micro. Science," 1878, p. 184. 



