534 PATHOGENIC AEROBIC BACILLI 
cholera group, the Bacillus typhi murium of Léffler, the bacillus of 
Laser, the Bacillus enteritidis of Gartner, and other similar bacilli 
appear to be differentiated from one another by characters which 
justify their description under separate names. Still it is difficult to 
fix upon any one of these characters to which specific value can be 
attached; and, in view of the many varieties found in nature or pro- 
duced artificially in laboratory experiments, we are not justified in 
asserting that our classification of these low organisms has any sub- 
stantial scientific foundation. The difficulties attending an attempt 
to establish specific characters are well illustrated by the extensive 
literature relating to the differentiation of bacilli belonging to the 
typhoid group from those belonging to the colon group. The main 
points upon which the distinction must depend have been referred to 
in the section devoted to the typhoid bacillus. 
Fremlin (1893) has made a comparative study of the colon bacil- 
lus from various sources. He finds the common characters of gas 
production in media containing sugar and coagulation of milk. Cul- 
tivated from different animals the morphology is the same, but there 
are differences as regards motility. The most active movements are 
said to be exhibited in the bacillus from man, while the variety ob- 
tained from the intestines of rabbits showed scarcely any movements. 
The different varieties displayed considerable differences in their 
growth upon potato. 
Dreyfuss (1894) finds decided differences in the pathogenic viru- 
lence of the colon bacillus from healthy individuals and from those 
suffering from various intestinal disorders. A culture from the dis- 
charges of a fatal case of cholera nostras proved to be exceptionally 
virulent—tested by intraperitoneal injections in guinea-pigs. Gilbert 
(1895), as a result of his extended researches, concludes that there are 
five principal types among the bacilli most nearly related to the colon 
bacillus: 1st. Bacilli which differ from the colon bacillus by their 
being non-motile. This type includes two varieties: one gives thick 
yellowish colonies upon gelatin plates and numerous gas bubbles on 
potato—this is the bacille lactique of Pasteur and the Bacillus lactis 
aérogenes of Hscherich; the other gives thin, bluish-white colonies 
and includes the bacille de l’éndocardite of Gilbert and Lion. 2d. 
Bacilli which differ from the colon bacillus by the fact that cultures 
do not give the indol reaction. 3d. Bacilli which do not cause the 
fermentation of lactose. 4th. Bacilli which are not motile and 
do not ferment lactose. 5th. Bacilli which are not motile, do not 
give the indol reaction, and do not ferment lactose. 
Theobald Smith (1895) gives the following account of his method 
of detecting bacilli of the ‘‘colon group ’’ in water : 
