It) APPLIED BACTERIOLOGY 



158° F. These are the ' thermophylic ' organisms, which 

 have been recently studied by Miquel, McFadyean, and 

 others. 



With regard to the conditions of life of the bacteria, 

 they may be divided broadly into two classes. When the 

 organisms draw their nourishment from some living body 

 or ' host,' they are known as ' parasites.' These are 

 further termed ' obligate ' parasites if they can only live on 

 this ' host.' If the bacteria draw their nourishment from 

 dead organic matter, they are called ' saprophytes.' These 

 are also divided into ' obligate ' and ' facultative ' sapro- 

 phytes. Thus, it will be seen that a parasite under certain 

 circumstances may readily become a saprophyte. 



Some of the more important saprophytes are those 

 organisms which play such an important and useful part in 

 our everyday life, such as, for instance, in the phenomena 

 of fermentation, and also as the putrefaction agents which 

 transform dead and decomposing organic matter into their 

 simpler elements, thus completing the great life cycle, and 

 rendering the dead and effete matter again ready for the 

 vital processes. 



Amongst other life manifestations of the bacteria may be 

 mentioned those which have the property of generating 

 colouring matter, though not chlorophyll. The bacteria 

 themselves are colourless and transparent, and the pigment 

 is merely formed as a product of their metabolism, especially 

 under the influence of light. Many of the bacteria give 

 rise to various gases and odours, particularly the anaerobic 

 organisms which give rise to very foul putrefactive gases, 

 (ammonia, sulphuretted hydrogen, etc.). The Bacillus 

 prodigiosus gives rise to a smell resembling that of tri- 

 methylamine. 



Micro-organisms have the property of producing various 

 changes in the medium on which they are grown. In many 



