3O THE STORY OF THE BACTERIA. 



because one can never be quite certain from a 

 microscopical examination of small portions of 

 a beef-tea culture, but that in some other part, 

 for he cannot examine it all, other forms of 

 bacteria may be present. 



Nowadays, although we find beef-tea very 

 useful on many occasions in cultivating the 

 bacteria, we most frequently make use of solid 

 foods. 



Boiled potatoes, which have been carefully 

 cleansed and sterilized that is, free from any 

 bacteria from the soil or air by steaming, are 

 usually first prepared. These are cut in halves, 

 with knives sterilized by heat, being held in 

 the fingers which have been freed from living 

 germs by washing with corrosive sublimate, 

 and placed under sterilized bell-jars or in tubes, 

 so that they may not be contaminated by the 

 accidental falling upon them of bacteria from 

 the air. Now, by means of a platinum wire 

 set in a glass handle, which has been sterilized 

 by heating to redness, a tiny bit of the bacteria- 

 containing material is conveyed to the cut 

 surface of the potato, and the latter is covered 

 again and set away for a day or two in a warm 



