INSTITUTE, PUSA, FOR 1917-18 127 



indoxyl producers and do not destroy any large quantity 

 of indican without hydrolyzing it to indoxyl. On the other 

 hand a large number of the bacteria found in the dirty 

 river water are active indican consumers and may, even in 

 twelve hours, destroy some 30 — 40 per cent, of the indican 

 present, thus reducing the yield of indigo to that extent. 

 In addition to this positive action the competition which 

 goes on between bacteria in any culture medium whether 

 natural or artificial, will seriously reduce the hydrolytic 

 action of the beneficial bacteria if the activities of the latter 

 are curtailed by the presence of superior numbers of the 

 inimical species or even of otherwise inert kinds. It was 

 found in 1917 that interference with bacterial control of 

 the fermentation was due sometimes to excessive numbers 

 of destructive bacteria and not infrequently to the presence 

 in the untreated river water of a sufficiently large number 

 of hydrolyzers to reduce the difference between the artifi-* 

 cially produced water content of these desirable organisms 

 and the natural one, and with it the yield of indigo, to in- 

 significance. The frequent, but not constant, occurrence 

 of this phenomenon provided an addition to the evidence 

 upon which the theory underlying this work is based, 

 namely, that the notable differences observed between the 

 vields of individual factories can be correlated with the 

 differences in the bacterial content of their water supply. 



Thus in the case of low yields we are confronted at the 

 outset with a condition and not a theory, the presence of 

 destructive, and the absence of constructive bacteria, and 

 the alteration of this condition is the object of our present 

 research. 



Two methods of attacking this problem appear to pre- 

 sent themselves ; the first and most obvious being the removal 

 of all deleterious bacteria from the water supply and the 

 second, the use of artificial cultures of such quantity and 

 vigour as to overwhelm the original population of undesir- 

 able bacteria. 



It is a well-known fact that bacterial numbers in water 

 can be greatly reduced by settling and still more so by pre- 



