194 ELEMENTS OF WATER BACTERIOLOGY 



and B. coscoroba, the three together usually making 

 up 75 per cent all the lactose-fermenting organisms 

 present. A very interesting point brought out in these 

 investigations was the occurrence of " epidemics," 

 of particular types which at certain periods become 

 suddenly frequent, usually prevailing in human faeces, 

 cow faeces and water supplies at the same time. (It 

 should be noted for the benefit of anyone studying 

 Clemesha's book that the tabular classification of the 

 colon group at the end contains a serious misprint. 

 B. lactis-aerogenes, B. gasoformans, B. coscoroba and 

 B. cloacae are there given as saccharose negative, 

 whereas they should be saccharose positive.) The 

 discussion in the text, however, appears to refer to the 

 orthodox MacConkey types. Clemesha (1912^) made 

 a number of experiments on the relative resistance of 

 the various lactose-fermenting types by placing faecal 

 emulsions, with or without sand, in shallow dishes 

 in the sunlight and at various intervals isolating 10 

 colonies of the predominant types and working out 

 their fermentative reactions. In general the experiments 

 showed B. coli to be the dominant form at the beginning. 

 It quickly disappeared, however, and after a few hours 

 B. lactis aerogenes, B. acidi-lactici, B. cloacae and 

 others appeared. At the end of the experiments, 

 often on the second day, B. Griinthal or B. cloacae were 

 generally the only forms surviving. In a long series of 

 examinations of Red Hills Lake Clemesha obtained 138 

 colonies of lactose-fermenting organisms during rainy 

 periods and of these 59 belonged to MacConkey's 

 Group I, 10 to Group II, 14 to Group III and 55 to 



