1911. ] On Variation and Adaptation in Bacteria, 543 
tions they had “no hesitation in asserting that the reactions are remarkably 
constant” for any particular streptococcus examined. They admitted that 
the neutral red and salicin reactions showed some tendency to variation, 
and mentioned two instances in which the mannite reaction was lost after 
a week of culture on gelatin. But on the whole they found the tests 
appreciably constant. They stated that they had in a number of cases found 
them unchanged after so long as a year, quoting one instance in which the 
interval of observation was nine months. Other evidence which they gave 
of constancy is open to the criticism that it consisted in part of examples in 
which the reactions actually showed some degree of variation, and they 
accordingly suggested that “ slight differences in the composition of the media 
may possibly affect the series of reactions to some little extent.” Evidence 
is Offered here that greater differences in the media do actually affect the 
reactions to a remarkable extent. 
Using these test reactions Gordon found as many as 48 different chemical 
types among 300 streptococci from saliva, though it is to be noted that more 
than one-third of the number fell under three of the types. Houston found 
40 types among 300 streptococci from feeces. 
Andrewes and Horder, examining 228 strains of streptococci from man, 
referred them all to five types (one of which consists of pneumococci), but 
this was only accomplished by classifying no less than 173 of the strains as 
variants by defect and excess of one or other of the five main types selected. 
Their streptococcal types are named respectively pyogenes, salivarius, 
anginosus, and feecalis. 
The remarkable frequency of variants and the numerous gradations of the 
type forms are explained by Andrewes (if I understand him rightly) as due 
to the survival and persistence of intermediate biological links, connecting 
those main types in the “dominant genus” constituted by the streptococci, 
which will become distinct species if (and when) these variants disappear in 
the course of evolution. This view entails the supposition that the types 
and variants in question have definite and relatively fixed identities, and 
that the characters relied on for their differentiation have to some extent at 
any rate a specific significance. But it would seem to be an equally 
satisfactory alternative in an @ priorr explanation to suppose that the 
differences observed in the chemical reactions now under consideration are 
due to merely temporary and casual modifications of metabolism. It might 
further be suggested that the features of streptococcal activity which they 
concern are so extremely variable, and are so easily varied under the 
influence of varying environment as to be almost accidental in character and 
to afford no criteria of any differential value, nor any basis for a classification 
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