CHAPTER I. 



EXAMINATION OF LIVING BACTEEIA. — THEIR STEDCTUEE AND 

 FORM. HOW TO OBTAIN MATERIAL FOE EXAMINATION. 



Bacteeia are distributed everywhere in nature ; they 

 cling to the surface of every substance ; they are to be 

 found in fewer or greater numbers in dust, in water, 

 and in air. We only perceive their presence under 

 ordinary circumstances, however, when they find con- 

 ditions favourable for their rapid growth and develop- 

 ment. Generally they are detected by the odour they 

 produce ; sometimes, too, they impart a colour to the 

 substance upon which they are growing, or sometimes 

 they themselves acquire a coloration of their own, 

 when they are spread over the objects in thick, more or 

 less slimy masses. Although it is easy enough to find 

 bacteria in such masses, yet it is both simpler and 

 more convenient to grow the species to be examined 

 artificially, especially as this can be very easily accom- 

 plished in several difi'erent ways. Moreover, different 

 forms are obtained, according to the method adopted ; 

 and this, of course, is very useful in the study of bac- 

 teria. 



