236 MICRO-ORGANISMS AND FERMENTATION. 



under parallel conditions ; and lastly, a well-marked difference 

 between the species is noticeable in their behaviour towards 

 the wide range of nutrient liquids used in these branches of 

 industry (barley- and rye-mash, maize- and potato-mash, molasses, 

 etc.). Hence, it is essential that types suited to the existing 

 circumstances should always be selected. 



The condition of the product of fermentation exhibits con- 

 siderable differences, as has further been shown by the extensive 

 investigations of RAYMAN and KRUIS. 



Morphologically, the author finds that a curious difference 

 appears between the species used in practice, viz. : that they 

 are naturally grouped in two classes, of which one ("A") has 

 very short chains of cells, the buds being very soon detached 

 from the mother-cells; whilst the other ("B") exhibits large 

 chains consisting of many cells. This typical character has 

 remained unaltered in species which were isolated in pure 

 cultures ten years ago and used in practice. There does not 

 exist any direct connection between this morphological pheno- 

 menon and the nature of the fermentation, whether top or 

 bottom. 



BELOHOUBEK, SCHUMACHER, and WIESNER, have also carried 

 out microscopical and chemical investigations into these 

 yeasts, and BELOHOUBEK'S " Studien liber Presshefe" (Prague, 

 1876) contains specially accurate descriptions of the appear- 

 ance under the microscope of pressed yeast in the different 

 stages of its development, and observations on the microscopic 

 indications of the quality of manufactured yeast, so far as 

 can be judged from the cell-contents. The decomposing 

 yeast-cells show a change in the colour and consistence of their 

 plasma ; this gradually turns darker and liquid, the vacuoles 

 grow larger, and the sharp outlines between the vacuoles and 

 the plasma gradually disappear, the plasma shrinks from the 

 cell-wall and finally collects in irregular masses in the cell- 

 fluid ; these also disappear at last, and finally the cell- wall is 

 dissolved. According to these authors, cells also occur in 

 pressed-yeast, which suddenly develop a number of small 

 vacuoles ; these " abnormal vacuolar" cells quickly perish. 



