barber: heredity in certain micro-organisms. 37 



2. Bacillus typhosus. 



Iq the summer of 1904 a series of selections were made of 

 the long threads occurring in cultures of Bacillus typhosus, ex- 

 periments similar to those conducted with B. coli communis, and 

 carried on at the same time and under the same conditions. 

 A culture obtained from the collection of the Pasteur Insti- 

 tute was used, and the progeny of a single cell isolated at the 

 beginning furnished material for selection. 



A large number of abnormally long filaments were isolated, 

 several of which developed cultures exhibiting more than the 

 normal proportions of long filaments. Of these all but one 

 soon reverted to the type. This one showed the new char- 

 acteristics for some time and through a number of subcul- 

 tures ; but, being occupied with work on other organisms, I 

 did not follow the history of this race carefully, and it finally 

 died out. 



In the summer and autumn of 1905 I resumed these ex- 

 periments with a new culture of typhoid obtained from Parke, 

 Davis & Co. September 26 I isolated four cells of normal 

 appearance in four separate droplets ; three of these devel 

 oped normal offspring, but one gave rise to a new race char- 

 acterized by long filaments in much greater proportion than 

 the normal. Colonies on gelatin were much different from 

 those of the parent type cultivated under similar conditions. 

 They were very irregular in form, owing to the outgrowth of 

 long filaments, which formed subcolonies and gave the whole 

 the appearance of a group of small colonies. Bands of parallel 

 thread projected out from a colony, and sometimes curled 

 into peculiar spiral arrangements, owing probably to some 

 resistance met with in their outward progress. Fifty-three 

 days after its origin this culture had apparently reverted to 

 the type. 



At the same time that the above typhoid race was isolated, 

 a considerable number of isolations of long threads were 

 made; but all either failed to grow, or, after showing for a 

 time an increased proportion of long filaments, reverted to 

 the type. 



These experiments are incomplete, but from them it ap- 

 pears that variations appear in B. typhosus, which, when iso- 



