CHAPTER LI. 



CULTIVATION AND REPRODUCTION OF YEAST. 



264. Hansen's Method of Single-Cell Culture. 



IN samples of yeast as they reach the laboratory from natural 

 sources or from the fermentation industries, the cells are not 

 infrequently in an enfeebled condition, and therefore need to be 

 reinvigorated before they c?n be sowed in the nutrient gelatin 

 employed for making pure cultures. Thus in the case of 

 breweries, for instance, the usual practice adopted for sending 

 yeast samples to a pure-culture laboratory through the post is 

 to place a drop of the thick balm, about the size of a pea at the 

 most, on a sterilised filter-paper, and thus free it from water to 

 a sufficient extent to enable it to be sent, enclosed in several 

 layers of the paper, in an envelope. On reaching the laboratory 

 this desiccated drop is placed in wort, where the cells are revived 

 and regain their full power. The same thing is done in the case 

 of wine lees. The reinvigorated sample is then subdivided, in 

 the manner described below, in order to obtain cultures that are 

 indubitably grown from a single cell, and are therefore termed 

 " single-cell cultures." 



The insecurity of the dilution method has already been pointed 

 out in vol i. (p. 125); and for the purpose of obtaining pure 

 yeast cultures, this method was improved upon by E. CHB. 

 HANSEN (II.) in 1879. Hansen had observed that when several 

 cells were present in a culture vessel they settled down separately, 

 when properly stirred, and being devoid of locomotive power, 

 each developed into a colony by itself. In such cases those in 

 which only a single colony developed were alone suitable for the 

 purposes of pure culture. The first six species of Saccharomycetes 

 introduced into the literature by Hansen, namely S. cerevisice I., 

 S. Pastorianus /-///., S. ellipsoideus I. and //., were obtained 

 in this manner. At a later date (1883) HANSEN (XII.) made use 

 of the liquefiable solid medium, 10 per cent, wort-gelatin. J. 

 CHR. HOLM (IV.), in a critical investigation of the resulting 

 priority controversy, established the fact that this was done by 

 Hansen independently, and especially so with respect to the 

 method of R. Koch. 



As already stated in vol. i. (p. 132), it is only capable of fur- 



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