30 PURE CULTURES OF 



up to the spring of 1883, I stated (loc. cit.) that yeast cells 

 can be preserved in filter paper in some cases for twenty 

 months and in others for only five months. From more 

 recent experiments I have found that the cells do not com- 

 pletely perish in less than about five months, and that most 

 species do not survive after two years under the conditions 

 mentioned ; only one sample was still alive after two and 

 a half years. The experiments were made with young 

 vigorous cells, and the samples were kept in a drawer at the 

 ordinary room-temperature. It must be remembered that 

 with this method of preservation the yeast is introduced into 

 an envelope of filter paper. In this manner a pure culture 

 cannot, however, be preserved with certainty. When it is 

 desired to make use of the same principle, it is best to 

 employ the flasks containing cotton wool, and which will be 

 described below ; under these conditions several species often 

 form spores, and these will live longer than the ordinary cells. 

 For the reasons mentioned, flasks containing a solution of 

 cane sugar afford in general the best means for the preserva- 

 tion of yeast, and it is thus seen that there are no difficulties 

 in the way of preparing and keeping a whole series of tested 

 culture yeasts in zymotechnic laboratories, so that breweries, 

 distilleries, &c., can at any time be provided with the species 

 which they require. In Jorgensen's laboratory, for instance, 

 there is a collection of about 200 culture yeasts, and, according 

 to his verbal statement, none of these cultures in cane sugar 

 have died, although several of them are nine years old ; they 

 are kept in a room at the ordinary temperature which, espe- 

 cially in the summer, is fairly high. From these flasks the 

 yeasts, both high and low, desired by his clients are propa- 

 gated in beer wort. There was never any question of preserv- 

 ing these yeasts in ice. Mr. Petersen at Old Carlsberg, and 

 Professor Gronlund at New Carlsberg, have likewise success- 

 fully made use of the same method. Jorgensen states that 

 he made some experiments in order to ascertain whether he 



