CHARACTERISTICS OF THE COLON-AEROGENES GROUP 95 
tion of mannitol. The lactose fermcnting lqucfiers have always 
been grouped together as B. cloacue, and we are inclined to 
favor the retention of this arrangemeut until more conclusive 
evidence can be produced to support a revision. 
Although we have only a small number of cultures which 
produce only CO, in the anaerobic fermentation of dextrose, 
this character indicates such a fundamental physiological de- 
parture from the type that we have had no hesitation in 
putting them in a class by themselves. 
Active liquefaction of gelatin and the fact that 8 of the 12 
cultures included in this group failed to ferment lactose sug- 
gests the identity of this type with the proteus group. The 
three striking characteristics of the proteus group are the 
failure to ferment lactose, the liquefaction of gelatin and the 
formation of characteristic swarming colonics in gelatin. 
Two-thirds of our cultures agree with the first character and 
all with the second. he typical colony of proteus on gelatin, 
according to the original description by Hauser,’ has second- 
ary colonies which appear in the medium around the original 
colony. Evidently many cultures are classed as proteus which 
are not known to form this peeuliar type of colony. Herter 
and Ten Broeck?* mention one culture which did not form 
swarming colonics until it had been passed rapidly through 
a series of milk tubes and then plated on dextrose gelatin. 
We studied the colony fermentation of twenty-five liquefy- 
ing eultures on 5 per cent gelatin at 20°C. There was a great 
variation in the type of colony, and even in different colonies 
by the same culture on a single plate. Only a few of these 
twenty-five cultures formed what could be described as typical 
proteus colonies. In most cases the colony was round, with 
asmooth margin and without out-growths of any kind. Lique- 
faction appeared slowly, and the margin of the colony would 
be unliquefied. There were many exceptions to this, some of 
which are shown in Fig. 6. At @ is shown a single strand 
23 Gustav. Hauser, (ber Féulnissbacterien u. deren Beziehungen cur Sep- 
ticemie, Leipzig, 1885. 
2 C, A. Herter and C. Ten Broeck, A Biochemical Study of Proteus Vul- 
saris Hauser in Jour. Biol. Chem., 9, 6, pp. 491-511, 1911. 
