YEAST DEVELOPMENT. 297 



carried on by the former as by the latter. There is, how- 

 ever, just a slight difference in the size of the spores  or 

 cells (Plate I. Nos. 7, 8, 11), those from yeast being the 

 larger and more clearly spherical, with a greater number 

 of reproductive spores, — that is, cells with a single, clear, 

 nucleated cell in their interior, — while others are filled 

 with a darker granular matter, having only a slight ten- 

 dency to coalesce or become filamentous ; those from 

 achorion are for the most part ovoid, and very prone to 

 coalesce and produce elongated cells or torulae. With re- 

 ference to the slight difference in size, we must look upon 

 this as a matter of very little importance ; for to the pre- 

 sence of light in the one case, and its almost total exclu- 

 sion in the other, this difference, no doubt, is almost en- 

 tirely due. It would be more trustworthy if comparisons 

 of this kind could be made at the same stage of develop- 

 ment ; for be it remembered that yeast obtained from a 

 brewery is in a more favourable state, inasmuch as it is 

 stopped at a certain stage of growth or development, and 

 then set to begin its fermentation over again in fresh sup- 

 plies of a new pabulum, which give increased health and 

 vigour to the plant ; while, on the other hand, the 

 achorion, or Favus fungus, is obtained and used in an ex- 

 hausted state from an already ill-nourished or starved-out 

 soil. Neither can we attach much importance to differ- 

 ences in size and form of the spores, for even this occurs 

 in yeast ferment ; and although the ovoid is most fre- 

 quently seen in achorion, it is equally common to yeast 

 when exhausted. This is strikingly exhibited in Plate 

 I. No. 8, a drawing made from a drop of exhausted yeast 

 taken from porter ; here we have oval and elongated cells 

 with torulae. To ensure success in these and similar ex- 

 periments., the fungus or yeast should be left floating on 

 the surface of liquids ; the process is either carried on very 

 slowly, or is entirely arrested by submersion. 



Turpin and others, in their experiments on yeast, noticed 

 that the cells become oval and bud out in about an hour after 

 being added to the wort (fig. 159) ; but this change depends 

 as much upon temperature and density of the solution as 

 upon the quality of the yeast. It is a well-ascertained 

 fact that when yeast is added to distillery wash, which is 



