RESEARCHES ON YEASTS. 95 



In this connection, it may be well to remind the reader 

 that a yeast growth does not behave like a uniform chemical 

 mass, but that, on the contrary, it consists of individuals ; and 

 these, as is the case with organisms in general, differ more 

 or less from one another. These individual differences may 

 show themselves in the power of effecting clarification in a 

 more or less satisfactory manner. Since we take the single 

 cell as our starting point in the preparation of our pure 

 cultures, the growths which we obtain represent the in- 

 dividual peculiarities occurring in the species. If we test 

 these growths separately, we are often enabled to propagate 

 a race which is especially characterised by its clarifying pro- 

 perties. 



In the first German edition of this book (1888), I gave an 

 account of some other individual peculiarities which may 

 occur in low-fermentation brewery yeast. Here I will deal 

 with those which manifest themselves in the form of the 

 cells. From this standpoint the question is one of practical 

 importance when we have to deal with the preparation of 

 pure cultures. In the method which I have described, the 

 starting point is always a single cell. Let us assume that 

 we have obtained an absolutely pure culture of Carlsberg 

 yeast No. I ; I take this species because it was used in 

 most of my experiments. Some cells of this pure culture 

 are shaken up in wort gelatine, and a little of this is spread 

 over the under surface of the cover glass of a moist chamber ; 

 those cells are then located the positions of which are such 

 that the colonies to which they give rise will not grow into 

 one another. The resulting colonies, each of which we con- 

 sequently know for certainty to have sprung from a single 

 cell, are often very different, some consisting of cells which, 

 on account of their elongated and sausage-shaped forms, 

 would be described by Reess as Sacch. Pastorianus, whilst 

 others have the form which we generally regard as belonging 

 to Sacch. cerevisice ; and yet both belong to the same species, 



