35 



stained with a colouring agent. These bodies are 

 known by the name of bacteria or bacilli, and, 

 whilst some difference of opinion has existed, it is 

 generally thought that they are organisms belong- 

 ing to the vegetable kingdom. There is nothing 

 in their appearance to strike the observer that they 

 possess any significance, and yet by recent research 

 it has been found that they play a most important 

 part as constituents of the living world. The 

 character from which they mainly derive import- 

 ance is the facility and rapidity with which they 

 become developed. This contributes to their wide 

 distribution and counterbalances their minuteness. 

 It is only recently that the life of these organ- 

 isms has been known to produce effects of any 

 particular interest to us. Some while ago they 

 gave rise to a discussion upon the subject of 

 spontaneous generation which was carried on 

 throughout several years with at times a consider- 

 able amount of warmth. The fact had been 

 observed that when a liquid containing organic 

 matter was exposed to the air, it more or less 

 quickly, according to the prevailing temperature, 



C 2 



