Glucose and Mannitol hy B. coli communis. 



83 



by acid, as will be seen from the experiments described in Part III. 

 But with the method of studying the fermentation now employed there is a 

 very simple method of getting over the difficulties which might arise from 

 the presence of residual unfermented substance difficult to estimate. It 

 consists in so adjusting the weight of bacteria employed that, in the time 

 during which the experiment is to be continued, the whole of the substance 

 to be examined will be fermented. It is thus possible to control the fermenta- 

 tion in a way which was not possible in the earlier experiments and it should 

 be possible to study the fermentation of carbohydrate and allied substances 

 for which no methods are at hand for their estimation with accuracy, as, for 

 example, the various polyhydric alcohols. The method has been used here 

 for the comparison of the products from mannitol with those from glucose 

 under the same conditions. 



The Neuiralisation of the Medmrii hy Ghcdlc. — Even if the fermentation flask 

 be repeatedly shaken during the course of the fermentation, there will be 

 periods during which the chalk will settle to the bottom of the flask if, as in 

 the usual experiment, the fermentation be continued overnight without 

 agitation. During such periods the acidity may increase sufficiently to impede 

 or alter the course of a fermentation. The writer has employed a very simple 

 device for preventing the settling of the chalk during the experiment. It 

 consists in introducing the chalk into small sacks of cloth, in each of which 

 is placed also a small piece of cork. The weights of chalk and cork are so 

 balanced that the sacks just sink to the bottom of tlie flask when they are 

 first introduced ; during the course of the fermentation the acid disengaged 

 penetrates the sacks and they become swollen with gas and rise to the top of 

 the solution. During this movement up and down the chalk contained in 

 the sacks becomes gradually liberated, so that the solution is always turbid 

 with chalk witliout being mechanically agitated from without. 



Tlce Fermentation of Glucose in the Presence of Ghalk hy an Emtdsion of 

 B. coli communis. — A series of experiments will be now described in which an 

 emulsion of B. coli commnnis\YeLS allowed to act for a period of 48 to 68 hours 

 on a solution of glucose in distilled water, containing varying quantities of 

 potassium sulpliate. The fermentations took place in the presence of chalk. 



An accidental rise in the temperature during the early stage of one of the 

 first experiments (No. 3) gave rise to a phenomenon which has not since been 

 repeated to the same extent. The bacteria introduced into the fermentation 

 flask contained 0"5 grm. of fatty or waxy material. At the end of the 

 experiment the weight of this material was 3-5 grm. There had been thus 

 a synthesis of 3 grm. of a material which, under normal circumstances, 

 does not accumulate. On the contrary, in most experiments the amount 



