22 BACTERIOLOGICAL INTRODUCTION 



spore only is formed within a single cell, but each 

 cell does not necessarily form a spore. 



The spore stains with difficulty and retains the 

 stain, when once tinged, with considerable tenacity, 

 so that it is possible to stain the spores and the 

 body of the cells with contrasting stains. Fig. 12 

 is prepared in this way, the spores being red and 

 the cells blue. Owing to the contrast between the 

 strongly stained spores and the pale cell body, 

 the latter appears narrower than the spore, but 

 this is not really the case, as a comparison with 

 unstained specimens at once shows. 



The differences in the morphological characters 

 of the various Schizophytes are frequently slight 

 and variable, and in order to distinguish between 

 them, advantage is taken of variations in the mode 

 of growth on various media. Some liquefy gelatine, 

 some do not ; some form radiating colonies, others 

 regular and circular colonies ; some are granular, 

 others structureless ; some pigmented, others colour- 

 less. Many illustrations of the so-called charac- 

 teristic growths of organisms on various media are 

 given throughout the book. To permanently record 

 the characters of the surface colonies of micro- 

 organisms, preparations known as " impression 

 preparations" are made. Such a one is shown in 



