162 
BACTERIOLOGY: E. O. JORDAN 
a short time may convey superficially the impression of an environmental 
modification similar to that observed in an individual organism trans- 
planted into different surroundings, when in reality there has been sim- 
ply ehmination of unsuited variations and a selection of the variety 
adapted to the particular conditions. This is a serious obstacle in the 
way of obtaining a proper appreciation of direct environmental influence 
upon the individual bacterial cell. 
The great majority of bacterial variations that have been described 
belong to the class of apparently adaptive modifications, whether such 
modification be considered as due to the direct action of the environ- 
ment upon thousands or millions of bacterial cells, or to the superior 
advantage in the intra-cultural competition possessed by those cells that 
have some new peculiarity such, for instance, as that of fermenting a 
particular carbohydrate. A bacterial culture, brought in contact with 
a carbohydrate that it is unable to attack, may undergo a change so 
that it becomes able to split the carbohydrate, the change being then 
apparently adaptive. Such cases have been frequently cited as instances 
of bacterial mutation, but, as many of them are described, they might 
equally well be regarded as due to selective acting upon the so-called fluc- 
tuating variations. It is worth noting that most or all the cells of certain 
species seem to behave in the same way in the presence of certain fer- 
mentable substances, and that the newly acquired property is sometimes 
permanent for a long series of generations on other media, sometimes 
lost. 
In the course of some experiments I have been carrying on during the 
past three years I have attempted to determine the width of swing in a 
pure line strain of bacteria, B.coli, cultivated under varying conditions. 
From a freshly cultivated feces culture a single cell was isolated by the 
Barber method, and from the descendants of this cell, numbering some 
hundreds of millions, two other cells taken at random were made the 
parents of two strains which have been used in a long series of experi- 
ments. Without space left to consider the technical details the following 
results may be stated. Both strains have been subjected to a series of 
influences, some of which might be expected to lead to particular adap- 
tive modification, others of which were of a less specific character. Nei- 
ther strain in the course of growth for over 500 generations at 37° C. 
(transfer every two days) on ordinary nutrient agar has shown any per- 
manent change in ability to produce indol, to coagulate milk, or to 
ferment carbohydrates. On several occasions, however, variations in 
indol production were observed (four days at 37° C. — Ehrlich method) 
