HEMIASCOMYCETES 275 



delicate membrane, and thus the spores are formed stand- 

 ing free in the remainder of the protoplasm. 



* 10. The spores are at first very small, but they soon 

 increase in size ; the surrounding protoplasm becomes 

 used up ; the spore membranes increase in thickness until 

 at last in the mature condition they completely fill the 

 mother-cell. 



' ii. In S. Ludwigii and S. pastorianus the structure of 

 the nuclear apparatus is similar to that in S. cerevisiae, 

 and its division during the process of budding appears to 

 be also the same.' 



The above remarks apply more especially to S. cere- 

 visiae, S. cerevisiae Hansen i, S. Ludwigii^ S. pas- 

 torianuS) S. Mycoderma. Compressed yeast, and a red 

 yeast found in the air of the laboratory, were also 

 examined. 



Biichner has shown that the alcoholic fermentation of 

 sugar induced by yeast is due to the activity of an enzyme 

 or soluble ferment, which, by a special method of treatment, 

 can be extracted from the yeast-cell. Green has corrobo- 

 rated this observation, and points out that the enzyme is 

 only secreted while the yeast-cells are active, or during 

 actual fermentation. 



Symbiotic relationship between yeasts and bacteria is 

 not uncommon, and such dual compounds not unfrequently 

 promote fermentation. Kephir, a derivative of milk, and 

 a weakly alcoholic effervescing beverage, usually made from 

 mare's milk, has been used for centuries in the Caucasus. 

 The ' kephir grains ' with which it is prepared contain both 

 a bacterium and a yeast. The yeast cells secrete an enzyme 

 (lactase) that converts the milk sugar into grape sugar, 

 which is then further broken up by fermentation into 



