250 MANUAL OF POISONOUS PLANTS 



Saccharomyces. Meyen. Yeast 



Vegetative cells spherical, ellipsoidal, oval or pear-shaped, occasionally 

 elongated mycelial like; asci spherical; ellipsoidal or cylindrical with 1-8 asco- 

 spores 1-celled spherical or ellipsoidal. About 40 species. The S. apiculatus, 

 Rees, is important in the fermentation of fruit. The S. elUpsoideus causes 

 the fermentation of wine. The S. mycoderna, Rees, forms a white mass on 

 cider, wine, cucumbers, etc., and prepares the way for the acetic acid ferment- 

 ation. The 5". kefyr, Beyerinck, along with Bacillus acidi-lactici and other bac- 

 teria is found in Keyfr grains. 5". glutinus Fres., the pink yeast, is found 

 growing on nutrient media in laboratories. 



Saccharomyces cerevisiae, Meyen. Common yeast 



Vegetative cells, spherical or oval, 8-10x8-12 /i singly, or in several, budding 

 chains with one or more vacuoles; asci spherical or short elliptical 11-14, gen- 

 erally with 4 ascospores tetradform. It produces a white growth on gelatine 

 and potato, does not liquify the gelatine; causes fermentation of grape sugar, 

 maltose and cane sugar. The biology of the fermentation of beer is as fol- 

 lows : Barley, which is ordinarily used for this purpose, is allowed to germ- 

 inate; during the process of germination the starch, by means of diastase, is 

 converted into sugar, the sugar being afterwards removed with the water; this 

 sugary fluid is then placed in large vats in dark rooms at a comparatively 

 low temperature; the yeast plant is added and fermentation starts. 



The fermentation of sugar is due to an enzyme found in the yeast plant, 

 to which Buchner has given the name of Zymase. This enzyme breaks the 

 sugar into alcohol and carbon dioxid. It is not necessary to have the living 

 organism present to produce this fermentation, as a quantity of the yeast ex- 

 tract mixed with the solution of fermentible sugar will produce at the end of 

 some days a small amount of alcohol. The enzyme decomposes very rapidly. 

 Reynolds Green, in his book on fermentation, says : 



From these researches it appears certain that the production of alcohol whether in the 

 presence or absence of oxygen is brought about by the activity of an enzyme. Its secretion 

 by the cells of yeast attends the ordinary nutritive processes as well as the abnormal de- 

 compositions set up by incipient asphyxiation. The latter condition induces its formation 

 in other parts of plants. The absence of oxygen stimulates the protoplasm of the cells to 

 secrete it, the ultimate effect of its appearance being the liberation of energy as already 

 stated. 



Distribution. Widely distributed. 



Poisonous properties. The chemical composition of alcohol is C^ H^ OH. 



Different alcoholic drinks contain different percentages of alcohol. Ale and 

 beers contain from 4 to 8 per cent together with bitters and malt extract ; cider 

 from 5 to 9 per cent; sherry from IS to 20 per cent. 



Fig_. _ 77. Yeast. Saccharomyces 

 cerevisiae. Ascospores in cells. Spores 

 at /. Magn. 1000. After Hansen. 



