fot 1.) On Variation and Adaptation in Bacteria. 545: 
put forward that particular strains of any given type of micro-organism, 
such as Streptococcus, can be regarded as distinct and fixed varieties on the 
results of any given series of culture tests requires to be most carefully 
scrutinised before it can be accepted, and the constancy of the reactions 
concerned must be thoroughly assured. 
As regards the streptococci, however, the observations which I have 
carried out appear to show that this is not the case. If cultures of these 
organisms are examined at considerable intervals of time their reactions in 
the test media are by no means constant, but on the contrary are found to 
undergo remarkable changes. Further it is found that such comparatively 
simple manipulations as continued culture in a particular medium may 
entirely alter the reactions of these organisms not only to that medium 
itself, but (it may be) to others also of the carbohydrate media. 
METHODS. 
The streptococci to be examined were first plated out twice to ensure as 
far as possible that the culture obtained arose from a single individual or 
chain of individuals. With the exception of the one named E below 
(cultivated from horse-dung) they had all been isolated from the human 
subject. 
The stock cultures of these organisms were propagated in stab agar, and 
sub-cultures were established every seventh day. 
The test media were prepared as directed by Gordon, at first with ordinary 
bouillon freed from sugar, but later, and for the bulk of the results recorded 
below, from “lemco.” With each series of cultures in a particular test medium 
an uninoculated control tube of the same medium was put up, and incubated 
with them for comparison. Whenever a negative reaction was obtained, a 
sub-culture from the negative tube was prepared in ordinary bouillon in order 
to make sure that the organism had actually grown in the test medium. If 
growth was not obtained in this sub-culture, the test was repeated. 
In the tables given below, the sign + indicates the production of an acid 
reaction under the test conditions (and where milk is concerned, the formation 
of a clot), while the sign 0 indicates that the reaction remained alkaline (or 
milk unclotted, whether it remained alkaline or became acid in reaction). 
The former may be spoken of as a positive, and the latter as a negative 
reaction. The neutral red test, which is admitted to be somewhat variable, 
was usually omitted ; and coniferin, which could not be obtained commercially, 
was not used. 
