BARBER: HEREDITY IN CERTAIN MICRO-ORGANISMS. 27 



room or refrigerator temperature than in the incubator. 

 But whatever the conditions under which the new race is 

 made to assume a more nearly normal aspect, it returns to 

 the filamentous type when brought into conditions favoring 

 this type ; and the new characteristics have persisted unim- 

 paired through a period of two years and eight months' cul- 

 tivation. 



In order to further ascertain the fixity of the new race a 

 selection experiment was carried out. This experiment ex- 

 tended over several days and was conducted in drop cultures. 

 In one series selections were made of the shortest elements 

 of the new race, always selecting cells resembling the normal, 

 and in the other series the longest filaments were selected in 

 a similar manner. When a considerable growth had been 

 obtained the shortest were again selected from the offspring 

 of the short, and longest from the long. 



These series were conducted through six selections of the 

 longer filaments and six of the shorter. At the conclusion of 

 the experiments there was no difference apparent between the 

 two types, both having the usual appearance of the new race 

 A. So it is evident that selection from either extreme of the 

 curve of variability does not produce a race of different mean ; 

 there was neither accentuation of the peculiarity nor return 

 to the original type. 



Indol formation was tested in Dunham's peptone broth, 

 about three months after the origin of race A. The color re- 

 action was approximately the same for each type, and it is 

 concluded that the new race forms indol in about the same 

 degree as the parent form. 



One of the most striking cultural characteristics of race A 

 is its increased power of fermenting sugars. 



In order to obtain more reliable quantitative results two 

 new sorts of fermentation tubes were devised, one of which 

 (tube No. 1) has already been described under the yeast ex- 

 periments. In the other sort (tube No. 2) gas is formed 

 under pressure exerted by a column of mercury. The mer- 

 cury is poured into the apparatus until it enters the lower 

 part of chamber a (fig. 2). Nutrient fluid containing the 

 sugar to be fermented is then poured into chamber a through 



