ALGJE 249 



spores remaining unstained. For permanent preparations 

 the moulds are best mounted in glycerine jelly, the cover- 

 glass being ringed with varnish to preserve the specimen. 



Culture of Moulds. — Hansen recommends the addition of 

 O'l to 0"2 per cent, of hydrochloric acid to the culture 

 medium, in order to restrain the growth of bacteria. 



A number of the minute water-plants known as the algae 

 are included with the micro-ojganisms. They are classed 

 in two main divisions, Leptotricheoe and Cladotrichece. 



The Leptotrichece are divided into three genera, viz., 

 Crenothrix, Beggiatoa, Leptothrix ; the CladotrichecB are 

 included in a single genus, Cladothrix. 



(a) Crenothrix. — These are very common in running or 

 stagnant water. They form simple threads, the separate 

 cells of which surround themselves with a distinct sheath, 

 and then change themselves by segmentation at their ends 

 into roundish spores. The threads are motionless, and, 

 especially in their younger stages, group themselves into 

 little patches. The most important member of this group 

 is the Crenothrix Kuhniana. 



Crenothrix Kuhniana. — This is very frequently found in 

 water containing organic matter or iron. It sometimes 

 occurs in such great numbers that the water is unusable 

 owing to the unpleasant odour and taste it produces. The 

 organism produces a thick vegetable mass in the water, either 

 brown or greenish in colour, frequently imparting a reddish 

 or greenish tint to the water, and is capable by its presence in 

 reservoirs of deteriorating large quantities of water at a time. 



In microscopical appearance it exhibits, according to 

 Zopf, both cocci and rod forms, as well as filaments. The 

 cocci become invested with a gelatinous material, and 



