SECTION V. 



THE HEAT-RESISTING BACTERIA. 



THEIR PLACE IN NATURE AND THEIR IMPORTANCE IN THE 

 FERMENTATION AND FOOD-STUFF INDUSTRIES. 



CHAPTER XVII. 



BACILLUS SUBTILIS AND ITS CONGENERS. 



107. Roberts' Heat Method. 



THE unfavourable conditions to which the bacteria inhabiting 

 the soil are therein exposed result in the accumulation of such 

 species as are capable of developing reproductive forms endowed 



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 membrane swells up and the spores are liberated. 

 F, progress of spore-germination. B-F, magn. 600. (After Brefeld and Zopf.) 



with great vitality. These are carried from the surface soil on to 

 plants, and in this way hay becomes infested with the spores of 

 highly resistant Schizomycetes, which can withstand the tempera- 

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



170 



