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CLASSIFICATION OF DAIRY BACTERIA. 183 
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others are Bacilli. But because of their practical association together in dairy 
problems, we think it more convenient to consider them all in one group, only 
referring to them in their logical place in our scheme of classification. The 
other gas producers, clearly not related to these, are described under the differ- 
ent groups where they belong. 
Two somewhat extensive studies of the acid-producing, rod-shaped’ bacteria 
have been made besides our own. One of these was by Harrison, who studied 
fifty-six different cultures (Cent. f. Bac. II., XIV. 359, 1905), and the second 
by Gruber who carefully studied thirty-seven cultures (Cent. f. Bac. II., XVI. 
654, 1906). Although these differ in some slight respects, the general conclusion 
from their study is in essential agreement with our own. There exists a long 
series of these forms that show slight variations, which grade into each other in 
such a way as to make it, at present at least, out of the question to arrange them 
all in any logical scheme even if it were worth while. Both Harrison and Gruber 
agree that all of these types may be arranged between two extremes, represented 
by Bact, lactis aerogenes and B. coli communis. The essential differences of 
the extremes are as follows: &. Jactis aerogenes is non-motile, produces no indol, 
and has a thick colony on gelatine; B. coli communis is motile, produces indol, 
and athin colony. But even these primary characters cross each other more or 
less, especially those of indol production and the type of colony, so that they 
cannot be regarded as especially characteristic. Indeed, almost any combina- 
tion of the above characters as well as others can be found among the many 
cultures that have been studied. 
Whether, under these conditions, it is worth while to attempt any-classifica- 
tion may well be doubted. Harrison does divide them into a series of groups 
without, however, implying that his groups have any diagnostic significance. 
In doing this he recognizes all the variations he can find between the different 
cultures studied, with a result of making a confusing series of types that clearly 
have no very great value. 
Gruber endeavors further to divide these organisms into groups by their power 
of fermenting a long series of carbohydrates, and finds it possible to recognize 
four types. But each of the four is found among both the aerogenes and the 
coli type, so that the plan is not particularly useful, quite independent of the 
fact that no other obsérver has made test with this long list of sugars. 
The sum and substance of the matter is, that there is no means at our 
command at present by which we may satisfactorily group these types into 
definite subdivisions. The plan we have adopted is very simple. We recog- 
nize, first, the typical aerogenes type, under which we have referred to a number 
of the variations that are known to occur. Then we recognize a type with 
flagella, but with the typical luxuriant aerogenes colony. Third, a type with 
the typical cof characters but monotrichic, and lastly, the typical co/z form 
with its peritrichic flagella. 
Gruber states that in the cold types studied by him, the flagella were always 
monotrichic and that the name Bacillus should be changed to Pseudomonas. 
In our own work we have found both the monotrichic type and the peritrichic 
type. The peritrichic type has appeared far more frequently than the mono-’ 
trichic type, but the latter has been found quite a number of times. Whether 
these modifications are the same or really two different types of colt, we do not 
