INSTITUTE, PUSA, FOR 1918-19 111 



lization of the water and plant as an alternative to hot 

 water extraction ; this would be a very much cheaper method 

 of eliminating undesirable bacterial flora than -the use of 

 hot water, but it is not yet clear whether it will be possible 

 to obtain the high percentage extraction of indican given 

 by the latter process. 



A point of great practical interest arose during the first 

 days of manufacture. It was found that owing to the 

 " weathering " of the cement-lining surfaces of the vats 

 during the months intervening between one manufacturing 

 season and the next following one, lime was set free by dis- 

 integration in sufficient quantity to produce an alkaline 

 reaction in the steeping water of such a degree as to inter- 

 fere seriously with the growth and activity of the hydroly- 

 zing bacteria; in this way fermentation was delayed to 

 such an extent that even after twelve hours this process 

 then normally complete was only just beginning. It was 

 found necessary to add considerable quantities of acid 

 (250 c.c. of 50 per cent, sulphuric acid per 600 gallons) to 

 neutralize this alkalinity. There can be no doubt that a 

 similar action takes place in all factories using cement- 

 walled vats, and that the "warming up " of the vats com- 

 monly noticed at the beginning of each season is due partly 

 to the removal of the disintegrated lime from the walls as 

 well as to the gradual establishment of the necessary bac- 

 terial flora. 



It is of interest to note here that numerous reports have 

 been received from indigo factories of improved yields 

 resulting from the use of cross walls or other methods of 

 increasing the wall area of the vats, recommended (1917-18) 

 as a result of the discovery of the importance of bacterial 

 .action in the fermentation of the indigo plant. 



V. Pebrine. 



Further study of the problem of elimination of this 

 disease of the silkworm in India, included trial of the effect 

 of hill-rearing upon the natural resistance of the larva to 



