222 MICRO-ORGANISMS AND FERMENTATION. 



From this description of the microscopic relationships of 

 these two types of bottom-yeast it must on no account be 

 assumed that we are able, by means of a microscopic examina- 

 tion of an unknown species of yeast, to determine whether it 

 will give a high or low attenuation, or whether it will clarify 

 slowly or quickly, etc., etc. HANSEN'S and the author's 

 investigations have, on the contrary, proved that it is impossible 

 to establish any general rule ~by this means, for species which give 

 a high attenuation may have the same microscopic appearance 

 as species which give a low attenuation. It will only be 

 possible to form an opinion of this character when our know- 

 ledge of the structure of the plasma is much more advanced. 

 Statements to the contrary which have hitherto appeared in 

 the literature of our subject are purely erroneous. 



The comparison carried out by WILL of four bottom- 

 fermentation yeasts may be instanced as a fine example of the 

 application of HANSEN'S biological methods for the distinction 

 of yeast-species. This comparison furnishes additional evidence 

 of the fact that there exist distinguishable species within the 

 limits of this group, as well as among those which have not 

 yet found application in the services of industry. In his 

 characterisation, WILL starts from the preliminary classification 

 of brewery yeasts suggested by the writer in the year 1886, 

 classing type 93 and 2 with the strongly fermenting, 7 

 with the feebly fermenting types, whilst type 6 is a yeast 

 of middle fermentation. The four yeasts may be described 

 as follows: 



Type 2 consists of large roundish or oval cells. Colonies on 

 gelatine, globular or lenticular. Spores numerous and readily 

 formed. Spore-formation at 11-31C. ; optimum, 2 5-2 6 C. 

 Film-formation at 7-3 1C. ; very slow. 



In type 6, oval cells predominate ; but this species has a 

 marked tendency to form sausage-shaped cells. Colonies on 

 gelatine, globular or lenticular. Spores readily formed. Spore- 

 formation at 11-31C. ; optimum, 28C. Film-formation at 

 7-30 C. ; slower than in type 7. 



The cells of type 93 are typically oval, passing, however, 

 generally into a roundish shape. Colonies in gelatine, globular 

 or lenticular. Spores readily formed. Spore-formation at 



