CHAPTER VI. 
THE PREVALENCE AND SIGNIFICANCE OF A CLASS OF ORGANISMS 
WHICH FERMENT GLUCOSE BUT NOT LACTOSE 
IN SURFACE WATERS. 
WATER analysts have long recognised that a class of or- 
ganisms which ferment glucose, but not lactose, is very common 
in water, so much so that it is still a debatable point whether 
a glucose or lactose bile salt broth is the best medium to use in 
endeavouring to obtain a rough estimate of fecal organisms 
present in water. In the original paper by MacConkey and 
Hill a bile salt glucose broth is recommended. Subsequently, 
however, the former of these authorities has stated that a 
lactose broth is better suited for the purpose, and that a glucose 
broth was used so as not to exclude bacillus of enteric, 
and the Gaertner group. On the other hand, Dr. Houston 
is of opinion that a bile salt lactose broth is not suffi- 
ciently inclusive for the first step in isolating from water 
the large group of organisms which are probably feecal in 
origin. Following MacConkey’s advice our original work. 
at the King Institute, Madras, 1907-08, was done with 
lactose broth, but subsequently it seemed very desirable 
to investigate the use of glucose medium as well. So 
in July, August and September 1909 all routine samples, 
taken from water supplies all over the Presidency of Madras, 
were put through both glucose and lactose broth by separate 
assistants. This piece of work gave some very remarkable 
results, and showed the necessity for investigating the matter 
more thoroughly. As regards the method followed in this 
preliminary investigation very little need be said. The usual 
dilutions of 20, I0, 5, I, ‘1, ‘or of the water were made; one set 
being put into glucose and the other into lactose broth. 
From the 20 cc. tube a loopful was taken out, mixed with 
water and put on to abile salt neutral red lactose agar plate. 
From each sample a number of colonies were picked off at 
