100 STORRS AGRICULTURAL EXPERIMENT STATION. 
power of fermenting sugar may be taken as a valuable and 
important criterion in separating groups, there may be vari- 
ations among the members of this group in the kind of sugars 
they can ferment and the readiness with which they can carry 
on this action. At all events we believe that the variations in 
the power of fermenting sugar are only of value in separating 
closely allied varieties from each other, but quite insufficient 
to characterize different groups. 
The production of pigment by bacteria is one of the charac- 
ters frequently more striking than any other. The question of 
the value of this characteristic in separating organisms from 
each other has been much discussed. It has been many times 
shown that this power of producing pigment is capable of 
variation. It is certainly true that some organisms that are 
able to produce pigment under some conditions lose this power 
after cultivation. 2. rudensis, for example, which, when first 
isolated, produced a brilliant red pigment, wholly lost this 
power in cultivation, and when the organism had reached my 
laboratory many months from its original source, it was a pure 
white Bacterium, showing all the other characteristics of the 
genus, but having lost its pigment-producing power. If the 
power of producing pigment is thus capable of variation, it 
indicates, of course, that it is not a criterion to separate types 
radically from each other. Nevertheless, in the general study 
of micro-organisms this is one of the characteristics which must 
be taken into consideration. Even though we recognize that 
some pigment-producing organisms may, under conditions of 
long cultivation in the laboratory, be converted into non-pig- 
ment-producing types, it is none the less important for us to 
recognize the pigment-production as a distinct characteristic of 
the organisms as found in milk productions. 
For practical purposes it is a matter of less importance to 
know that a red pigment may cease to be developed after long 
cultivation in the laboratory than it is to recognize as a distinct 
type of dairy organisms a bacillus producing a red pigment. 
We have therefore used the pigment production as one of the 
characteristics for separating our groups. From our observa- 
tions we have been inclined to think that red, orange, brown, 
and green pigments are commonly distinctively characteristic, 
that a lemon yellow color is also a character which remains 
