26 THE MICROSCOPE Feb. 



are various other products formed by the bacteria and 

 moulds that are present. 



I have been making some experiments on bread, using 

 pure cultures of yeast. Three different yeasts were used ; 

 one separated from a compressed cake, another from a dry 

 cake, while the third was obtained from what is known 

 as potato yeast, i. e., a culture of brewers' yeast in an 

 impure condition in potato solution. The form occurring 

 in greatest abundance in the cakes and solution respec- 

 tively being the ones used. 



Control experiments were carried on at the same time, 

 using ordinary compressed yeast. Best results were ob- 

 tained from the pure yeast gotten from the compressed 

 cake. The time and extent of fermentation were about 

 the same as that obtained in the control, but the some- 

 what sour odor one gets in ordinary dough was lacking, 

 and the bread was sweet to the taste. 



Some of the dough was kept, that of the control sour- 

 ing the second day, whereas the pure culture gave no in- 

 dication of souring at the end of two weeks. 



The results of the experiments are not so decisive as 

 they are suggestive of the possibilities for pure yeasts in 

 bread-making. A sufficient number of yeasts were not 

 used to determine the qualities which they would give to 

 bread, but sufficient was done to prove that the bread 

 from the pure culture was superior in many respects to 

 that from the impure yeast cake. 



In brewing, pure yeasts have been used, and that with 

 the most advantageous results ; to such an extent is this 

 true that Hansen's pure and selected races of yeast are 

 used in breweries in America, Europe, Asia, and Australia. 

 Apparatus has been devised by means of which yeast can 

 be transported to any part of the world in a pure condi- 

 tion, and also appartus for cultivating large quantities of 

 the yeast for pitching purposes. And, as it has been 

 determined that under brewery conditions, constancy of 



