SECTION V. 



TI1K II MAT RKSISTINd IJACTKIMA. 



TIIKIIl I'LACK IN NATTlii; AND THKIK I M I'OltTA V 'K IN TIIK 



r-Ki!Mi:\TATi<)\ AND FOOD-STI KF INDI-STHIKS. 



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 with great vitality. These are carried 

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



FK;. 40. Hacillus stibtilis. 



(J, a fragment of the skin funned on liny infusion, m.-imi. 200 times. Consists of tightly parked 

 !il;uuentury ^roups of cells. 15 and C show the individual parts of these threads at sin early sta-e. 

 1>. a thread, eaeh separate part of which contains an oval endospore. K, the mother-cell mem- 

 brane 8\vells up and the spores are liberated. F, progress of spore-germination. B-F, niagn. 600. 

 (Afl>-r ltr<feltl din/ Zopf.} 



the spores of highly resistant Sckizomycetes^ which c;in withstand the tempera- 

 ture of boiling water for several hours. Early observers, bt>ing unacquainted 

 with this property, noticed with astoiiishnieiit that a development of bacteiia 

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

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



131 



