316 APPLIED BACTERIOLOGY 



(2) Only young and vigorous cells can exercise this 

 function. 



(3) The most favourable temperature for most of the 

 species is about 25° C. 



(4) A few saccharomycetes form spores when present in 

 fermenting nutrient liquids. 



A small portion of a young and vigorous growth is trans- 

 ferred to a moist gypsum block, prepared as follows : To 

 well-baked plaster of Paris add distilled water until the 

 plaster is nearly liquid ; pour this on to a sterilised glass 

 plate on which rests a small mould of metal or paper. 

 The blocks are dried and sterilised. They are then laid in 

 a shallow tray containing a little sterile water, the whole 

 arrangement being kept well covered by a bell- jar. The 

 apparatus can be placed in an incubator if any special 

 temperature is required, or may be kept at the ordinary 

 temperature of the room. 



Hansen found that the formation of spores takes place 

 slowly at low temperatures, more rapidly as the tempera- 

 ture is raised to a certain point ; when this point is passed 

 their development is again retarded, until finally a tempera- 

 ture is reached at which it ceases altogether. The mass on 

 the plaster plate is carefully examined from time to time. 

 After a certain lapse of time, which varies with the dif- 

 ferent species, roundish plasma particles appear in the 

 cells, and these are the first indications of spores. In 

 their further development they become surrounded by a 

 wall, which is seen more or less distinctly in the different 

 species. The spores may expand to such an extent that 

 the pressure which they exert on each other whilst they 

 are still enclosed in the mother-cell brings about the forma- 

 tion of the so-called partition-walls. During the further 

 development a complete union of the walls may take place, 

 so that a true partition-wall results ; the cell then becomes 



