222 CULTIVATION AND REPRODUCTION OF YEAST. 



latter culture vessel direct when use is made of a platinum wire, 

 about i cm. long and 0.5 mm. thick, held with a forceps and 

 sterilised in the flame just before using. 



Another result either subsidiary or as the main object 

 obtainable by means of the above method of reinvigoration, is a 

 purification of the sample. In this way MULLER-THURGAU (XX.), 

 for instance, in cultivating yeast destined for the fermentation of 

 red wine or perry musts (rich in tannin) and therefore required 

 to be able to stand the presence of large quantities of that sub- 

 stance, allowed the sediment forming the raw material to repro- 

 duce several times in red must or tart perry must. In this way 

 he effected a selection affording greater prospects of ultimate 

 success in the cultures afterwards prepared by the single-cell 

 method. 



P. LINDNER (XXI. and XV.) applied the name "small drop" 

 culture to a modification of Hansen's single-cell method. He 

 diluted the dissected sample to such an extent with wort that 

 a small drop of same contained only a single cell, and then, by 

 means of a very fine sterilised drawing-pen, made a number 

 of small drops or fine streaks on a sterilised cover-glass, which 

 was next fixed over a Bottcher cell or hollowed slide, by means 

 of vaseline, &c., and examined under the microscope, each 

 small drop found to contain only one cell being marked. The 

 resulting colonies are afterwards transferred to another medium 

 (wort-gelatin, wort). The shrinkage which takes place in cells 

 placed in the highly plasmolytic nutrient gelatin is here avoided, 

 and consequently the proportion of cells that will not develop is 

 reduced. Moreover the cells are more readily detected than is 

 the case with solid media, owing to the greater difference between 

 the refractive power of the cells on the one hand and the medium 

 on the other. F. SCHONFELD (II.) found it useful to combine the 

 externals of this method with the essential features of the Hansen 

 single-culture method, by treating a little of the sample (sludge 

 or sedimental yeast) with wort-gelatin and transferring small 

 drops and streaks of this mixture to a cover-glass which is after- 

 wards fastened down on a hollowed slide. 



Re-inoculation from a single-cell culture into a fresh nutrient 

 medium gives an absolutely pure culture. The labour devoted to 

 the latter has then a different purpose, more especially to deter- 

 mine whether it is adapted to the object in view, to select the most 

 suitable from a series of pure cultures, and finally to reproduce a 

 sufficient quantity for use in practice. 



A few remarks may be made, for the information of beginners, 

 on the best method of keeping pure cultures in the laboratory. 

 The most convenient, when feasible, is to leave the yeast covered 

 by the liquid in which it has been grown. This is only practicable, 

 however, when the operator has sufficient leisure or inducement 

 (in the way of orders for supplies of yeast) to re-transfer the 



