SECTION V. 

 THE HEAT-RESISTING BACTERIA. 



THEIR PLACE IN NATURE AND THEIR IMPORTANCE IN THE 

 FERMENTATION AND FOOD-STUFF INDUSTRIES. 



CHAPTER XVII. 



BACILLUS SUBTTLIS AND ITS CONGENERS. 



107. Roberts' Heat Method. 



THE unfavourable conditions to which the bacteria inhabiting the soil are 

 (herein exposed result in the accumulation of such species as are capable of 

 developing reproductive forms endowed with great vitality. These are carried 

 from the surface soil on to plants, and in this way hay becomes infested with 



FIG. 40. Bacillus subtilis. 



G, a fragment of the skin formed on hay infusion, magn. 200 times. Consists of tightly packed 

 filamentary groups of cells. B and C show the individual parts of these threads at an early stage. 

 D, a thread, each separate part of which contains an oval endospore. E, the mother-cell mem- 

 brane swells up and the spores are liberated. F, progress of spore-germination. B-F, magn. 600. 

 (After Brefeld and Zopf.) 



the spores of highly resistant Schizomycetes, which can withstand the tempera- 

 ture of boiling water for several hours. Early observers, being unacquainted 

 with this property, noticed with astonishment that a development of bacteria 

 occurred spontaneously in vegetable infusions (especially infusions of hay) that 

 had previously been exposed to boiling heat for an hour. The cells were almost 



