164 Lectures on Bacteria. [^ xiii. 



have of it to refer expressly to its facultative saprophytism. Its 

 saprophytic vegetation requires an abundant supply of oxygen. 

 If cultivated with this upon a suitable moist substratum it 

 developes rapidly and copiously, taking the place of any com- 

 petitors it may encounter; but after some days the energy of its 

 growth rapidly diminishes, perhaps in consequence of the dis- 

 turbing influence of its own decomposition-products. These 

 phenomena were most strikingly exhibited in cultures on moist 

 linen, which was selected for practical reasons. The optimum 

 temperature for vegetation is, as was stated above on page 50, 

 that of the body of a warm-blooded animal, about 37° C, but 

 20-25° C. is sufficient for good development. Death ensues 

 without fail in a fluid heated to 50-55° C. The Spirillum is 

 not killed by being cooled to or below the freezing point, even 

 if this temperature is maintained some hours. Perfect desic- 

 cation kills the vegetating Spirillum in less than twenty-four 

 hours ; the arthrosporous Spirilla on the contrary, according to 

 Hueppe's direct observation, continue capable of germination 

 for four weeks after desiccation. On the other hand, as it is a 

 matter of observation that new vigorously vegetating generations 

 may proceed from desiccated cultures after a longer period than 

 this, and for almost ten months, Hueppe suspects, on good 

 though not quite conclusive grounds, that the new growths 

 always spring from arthrosporous Spirilla, and that these are 

 the specifically resistent resting states of the Bacterium of 

 cholera. I have already said all that is here necessary con- 

 cerning the food-requirements of the Spirillum, and on the 

 unfavourable or even fatal effect upon it of the acid reaction of 

 the substratum. 



The phenomena in the life of the Spirillum, which have now 

 been described, supply the needful explanation of the chief facts of 

 experience in connection with cholera as an infectious disease, 

 especially its claim to be indigenous in India, its introduction 

 into other countries and parts of the globe, and the chief points 

 in the history of its diffusion there. It is true that something 



