ADDENDUM 177 



The titration method the estimation of the amount of acid 

 produced takes a good deal more time than the simpler pro- 

 cedure of recording the qualitative production of acid. A 

 careful study of the results obtained does not establish that any 

 additional advantages are gained by its employment. The fact 

 that acid is produced shows that the sugar, alcohol or glucoside, 

 has been split up, but the amount of acid produced largely 

 depends upon the suitability of the medium as a nidus for the 

 multiplication of the streptococcus strain tested. Hopkins and 

 Lang using the titration method found that the fermentation by 

 a given streptococcus ceases where a certain acidity is reached, 

 irrespective of how much acidity might be formed by the 

 carbohydrate decomposition. They found that the acidity pro- 

 duced by the same strains in the same medium varied, but were 

 unable to discover the reasons for this variation. 



Hopkins and Lang also tested 24 of their strains at 

 intervals of 8 to 34 weeks and found the reactions qualitatively 

 unchanged. 



The constancy of these fermentation and the other cultural 

 characters have been investigated by a number of workers. 

 With reasonably comparable technique the amount of constancy 

 has usually been high although considerable variations may be 

 induced by special methods. Broadhurst (1915) has investigated 

 this question very extensively and found that, for the most part, 

 inconstancy of characters was not marked. In one series of 

 tests with 134 cultures of various types and from a varfety of 

 sources and retested after considerable intervals upon the usual 

 Gordon media, the three and four months retests gave 63 and 

 64 per cent, of constancy results respectively. As might be 

 anticipated newly acquired fermentation powers were more 

 variable than those originally possessed. Under ordinary 

 laboratory conditions there was a greater tendency to gain 

 rather than to lose fermentation powers. Twenty-nine per 

 cent, gained the power of fermenting one or more substances 

 while 19 per cent, lost powers of fermentation. A strain that 

 lost a power usually regained that power later while one 

 which gained usually retained it. Broadhurst found that 

 morphological characters varied considerably with the medium 



s. w. 12 



