THE BLASTOMYCETES 165 



of which is between 22 and 25 C. It only produces 

 1-1-3 volumes per cent, of alcohol. 



Saccharomyces Anomalus. Found in impure brewery 

 yeast, on green malt, and on fruit. It is peculiar in that 

 the spores are hemispherical, with a projecting rim, and 

 are like a bowler hat. It forms but little alcohol. 



Saccharomyces Pyriformis. A yeast which, with a 

 symbiotic bacterium B. vermiforme was found to cause 

 the change in a solution of sugar and ginger produced by 

 the addition of the ' ginger- beer ' plant (Marshall Ward). 



Schizosaccharomyces Octosporus. Found on currants 

 and raisins. In the genus Schizosaccharomyces of Lindner 

 the cells are like yeast cells, but multiply by fission through 

 a septum formed across the middle of the cell, and not 

 by budding. Ascospores are also developed, in this 

 particular species being usually eight in number. 



Examination of Yeasts. 



Hanson's scheme involves the isolation of a pure 

 culture, and the observation of the time taken at various 

 temperatures to form ascospores and ' films.' 



1. Microscopical Appearance. The growths, after grow- 

 ing in sterilised wort for twenty-four hours, are examined. 

 When S. cerevisue and 8. pastorianus are mixed or other 

 varieties are present, little is to be learnt from a direct 

 microscopical examination. 



2. Formation of Ascospores. The formation of spores 

 in the saccharomycetes is regulated by the following 

 conditions: (a) The cells must be placed on a moist 

 surface, and have plenty of air. (6) Only young and 

 vigorous cells can exercise this function, (c) The most 

 favourable temperature for most species is about 25 C. 

 (d) A few saccharomycetes form spores when present in 

 fermenting nutrient liquids. 



A small portion of a young and vigorous growth is 

 transferred to a moist gypsum block, prepared as follows: 

 To well- baked plaster of Paris distilled water is added 

 until the plaster is nearly liquid; this is poured into a 

 small mould of metal or paper. The blocks are allowed 

 to set, dried, and sterilised. They are then laid in a shallow 

 tray containing a little sterile water, the whole arrange- 

 ment being kept well covered by a bell- jar. 



Two sets of cultures on plaster blocks are made, one 



