96 STORRS AGRICULTURAL EXPERIMENT STATION. 
in the following pages it will be seen that there is a white 
liquefying anda white non-liquefying group. In other respects 
these types resemble each other so closely that we are inclined 
to believe that they must be regarded as representing the same 
form, but two physiological varieties, one having lost the 
liquefying power which the other still retains. Similar vari- 
ability is especially true in regard to pigments. Our experience 
has convinced us that whereas some pigments, like brilliant 
reds and deep oranges and greens, are distinctive characteristics 
of groups, the pale yellow colors and the white pigments are 
so sure to run into each other by intermediate variations that 
they are of very little value in distinguishing types. In the 
following pages it will be seen that a white and a yellow type 
of coccus has been described and recognized as different groups, 
but the intermediate forms which we have found convince us 
that they are really practically the same thing with slight 
physiological variations. Even in the question of morphology, 
which is usually regarded as the most manifest criterion for 
distinguishing types, something of the same appears. The 
distinction between the short rods forms and the coccus forms 
is by no means a sharp one. Cultures which have been de- 
scribed in our own laboratory as short rods have been sent to 
other laboratories and been described as coccus forms. To 
eliminate the confusion arising in all of these ways is manifestly 
as yet impossible, but we have endeavored in the arrangement 
of groups given in the following pages to recognize the sharper 
distinctions and to state, where possible, the connections of the 
groups by intermediate forms which have been discovered. 
In our studies, as involved in the following pages, we have 
endeavored to work upon and describe only such types as. are 
usually found zz zature. Cultural varieties are not generally 
included in our list. ‘The work in our own laboratory and 
elsewhere has shown that by modifications of the culture con- 
ditions an endless series of modifications may be produced in 
the descendants of the same original stock culture. The power 
of producing pigment may be changed, the power of liquefying 
gelatin, the shape of the bacteria themselves may be quite 
modified by different culture methods. It does not fall within 
our purpose to include such cultural varieties. We are inter- 
ested, in this paper, not in knowing through what variations 
