536 PATHOGENIC ABROBIC BACILLI 
BACILLUS LACTIS AEROGENES. 
Obtained by Escherich (1886) from the contents of the small intestine of 
children and animals fed upon milk ; in smaller numbers from the faeces of 
milk-fed children, and in one instance from uncooked cow’s milk. 
Morphology.—Short rods with rounded ends, from 1 to 
2 in length and from 0.1 to 0.5 # broad; short oval and 
oft, spherical forms are also frequently observed, and, under 
68 certain circumstances, longer rods —3 “—may be developed: 
3° £é usually united in pairs, and occasionally in chains contain- 
ing several elements. In some of the larger cells Escherich 
. has observed unstained spaces, but was not able to obtain 
Fic. 147,—Bacil- any evidence that these represent spores. 
om gee 8 This bacillus stains readily with the ordinary aniline 
aoe colors, but does not retain its color when treated by Gram’s. 
oe method 
' Biological Characters. —An aérobic (facultative anaérobic), non-liquefy- 
ing, non motile bacillus. Does not form spores. Grows in various culture 
media at the room temperature—more rapidly in the incubating oven. 
Upon gelatin plates, at the end of twenty-four hours, small white colonies. 
are developed. Upon the surface these form hemispherical, soft, shining 
masses which, examined under the microscope, are found to be homogeneous. 
and opaque, with a whitish lustre by reflected light. The deep colonies are 
spherical and opaque and attain a considerable size. In gelatin stab cul- 
tures the growth resembles that of Friedlinder’s bacillus—i.e.. an abundant. 
growth along the line of puncture and a rounded mass upon the surface, 
forming a ‘‘nail-shaped” growth. In old cultures the upper portion of the 
gelatin is sometimes clouded. and numerous gas bubbles may form in the 
gelatin. Upon the surface of nutrient agar an abundant, soft, white layer 
is developed. Upon old potatoes, in the incubating oven, at the end of 
twenty-four hours a yellowish-white layer, several millimetres thick, is 
developed, which is of paste-like consistence and contains about the peri- 
phery a considerable number of small gas bubbles; this layer increases in 
dimensions, has an irregular outline, and larger and more numerous gas 
bubbles are developed about the periphery, some the sizé of a pea; later the 
whole surface of the potato is covered with a creamy, semi-fluid mass filled 
with gas bubbles. On young potatoes the development is different; a rather 
luxuriant, thick, white or pale-yellow layer is formed, which is tolerably 
dry and has irregular margins; the surface is smooth and shining, and a 
few minute gas bubbles only are formed after several days. 
Pathogenesis.—Injections of a considerable quantity of a pure culture 
into the circulation of rabbits and of guinea-pigs give rise to a fatal result 
within forty-eight hours. 
In his first publication relating to ‘‘ the bacteria found in the dejecta of 
infants afflicted with summer diarrhoea,” Booker has described a bacillus 
which he designates by the letter B, which closely resembles Bacillus lactis 
aérogenes and is probably identical with it. He says: 
“Summary of Bacillus B.—Found nearly constantly in cholera infan- 
tum and catarrhal enteritis, and generally the predominating form. It 
appeared in larger quantities in the more serious cases. It was not found 
in the dysenteric or healthy feces. It resembles the description of the Ba- 
cillus lactis aérogenes, but the resemblance does not appear sufficient to con- 
stitute an identity, and, in the absence of aculture of the latter for com- 
parison, it is considered a distinct variety for the following reasons: Bacillus 
B is uniformly larger, its ends are not so sharply rounded, and in all culture 
media long, thick filaments are seen, and many of the bacilli have the pro- 
toplasm gathered in the centre, leaving the poles clear. There is some 
ae 
