BY It. GRBIG-SMITH. 



89 



2001- 



and eoutrol. The quantity advisable to add was as yet unknown and tenth 

 normal sodium hydrate was used tentatively. This did not seem to improve 

 matters and after tlie ninth day 10 e.c* of N/1.85 sodium hydrate were added as 

 a stronger alkali was apparently needed. The quantity of alkali added to each 

 flask was capable of fixing 11!) milligrams of CO2, and as the yield was not 

 completely depressed it is clear that the alkali was taken up by the bark and 

 that it can absorb or fix much more alkali than the study of the aqueous extract 

 would lead us to expect (see p. 87). 



Text-fig 2. The Fermentation of Tan-bark. — Daily Yields of Carbon Dio.xide. 

 Unbroken line = test, broken line = control. 



A slight increase on the tenth day followed the addition of the alkali, but 

 on the ele\enth day the yield went down. This suggested that the amount of 

 alkali had not been enough, and accordingly 10 c.e. of N/1 sodium hydrate 

 were added to each flask. This quantity seemed to be about right for the yield 

 of gas began to rise immediately. Thus the thirty gTams of dry bark required 

 an amount of alkali e((uivalent to 16.4 c.c. of normal sodium hydrate to neutra- 

 lise the inherent acidity or, at any rate, that part of the acidity whicli hindered 

 the fermentative activity of the bacteria. This is equivalent to 54.7 c.c. of normal 

 alkali per 100 grams of dry bark. 



The control remained sterile until the last addition of soda. Apparently the 

 spores had not been destroyed by the heat sterilisation and had remained quiescent 

 until conditions of growth were made favourable by the alkali. The vegetating 

 bacteria added to the test at the start remained in the acid bark for some time, 

 but they slowly disappeared for on the twelfth day they were very few in number 



* This contained 0.22 milligrams of CO2 as impurity. 



