34 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



case a slight scratch is made on the surface of the gelatine 

 slope (Fig. 5 6, p. 24) by means of a platinum hook infected 

 with the organisms, i.e., what is called a * streak culture.' 

 Growths are of course best obtained when the hyphae are 

 well matured ; mould cultivations can be examined in the 

 hanging drop and their stages of growth and developments 

 studied therein. 



For the preparation of permanent specimens of moulds 

 some modifications are necessary in the usual staining process. 

 Owing to the presence on their surface of a very thin layer of 

 fat, moulds are not easily moistened with water. Before 

 mounting, therefore, a portion of the mould intended for 

 examination is immersed in alcohol, to which a little ammonia 

 has been added ; the mould can then be stained with methylene 

 blue, the filaments of the mycelium and hyphae taking up the 

 colour while the spores remain unstained. Special care must 

 be taken not to overheat the specimens by too rapid drying. 



Instead of Canada balsam it is better to use glycerine 

 in the case of organisms such as moulds and algae, infusoria, 

 etc., the cover glass being attached to the slide by a ring of 

 shellac varnish. 



