42 MICRO-ORGANISMS IN WATER 



CHAPTER II 



THE STAINING AND MICROSCOPIC EXAMINATION OF 

 MICRO-ORGANISMS 



THE great advances which have been made in our 

 knowledge of micro-organisms during recent years are 

 in large measure due also to the ingenious methods 

 which have been devised for facilitating their identi- 

 fication and microscopic study by staining them with 

 brilliant colours. 



This staining of microscopic specimens is of great 

 importance in many ways. Thus, firstly, it enables the 

 bacteria to be recognised amongst the most varied 

 surroundings in consequence of their particular affinities 

 for some dyestuffs, whereby they may be discovered 

 under conditions in which they would infallibly escape 

 notice if examined in their natural state. In the second 

 place, by the application of these colouring matters far 

 greater precision and definition is given to the forms of 

 the micro-organisms, and by their means even a certain 

 amount of internal structure may in some cases be 

 discerned. Again, inasmuch as the affinities of sub- 

 stances for particular dyes tuffs are dependent upon 

 their chemical nature, it is evident that the deportment 

 of micro-organisms towards these colouring matters 

 serves as a micro-chemical reaction by means of which 

 they can not only be distinguished from other bodies 

 with which they may occur in juxtaposition, but which 



