PRACTICAL BACTERIOLOGY. 



bacillus alone being able to withstand the heat. These 

 now begin to develop in a most vigorous fashion, for 

 the hay-infusion, which contains the spores, is in itself 

 a most favourable nutrient medium for the hay-bacil- 

 lus. As all other organisms have been killed, and 

 the cotton-wool stopper prevents the entrance of new 

 ones, a pure culture of the hay -bacillus is obtained in 

 this manner. To be sure, there is no longer any doubt 

 that, under the name of hay-bacillus, there are in- 

 cluded many different kinds of bacteria, which for the 

 most part are very closely allied. This, however, for 

 the present, need not be considered, as in the follow- 

 ing experiment we shall occupy ourselves with the 

 form and development of the different kinds, rather 

 than with their rigid classification, which will be 

 treated at some length in later chapters. 



Finally a comparatively pure original material for 

 bacteriological experiments may be obtained in the 

 following manner : — Slices about one centimetre thick 

 of cooked turnips and potatoes are placed for a time 

 in different places — in the open air, in a cellar, on the 

 ground, or in a sitting-room. They are left in these 

 places for two or three hours freely in contact with the 

 air, and are then further cultivated in moist chambers. 

 The moist chamber (Fig. 1), which has been successfully 

 used up to now, consists of two glass vessels, the upper 

 arid smaller one, which is supplied with a handle, 

 fitting closely into the under one. Before use, these 



