200 ELEMENTS OF WATER BACTERIOLOGY 



lactose, saccharose and raffinose he found to constitute 

 a natural metabolic gradient, in the order named, 

 fermentation of any member of the series implying 

 fermentation of those preceding it. Fifty-three per cent 

 of his strains fermented all four sugars, 5 per cent all 

 but rafnnose, 41 per cent attacked dextrose and lactose 

 only, and i per cent dextrose alone. 



