536 PATHOGENIC AEROBIC 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 fogces of 

 milk-fed children, and in one instance from uncooked cow's milk. 



Morphology. Short rods with rounded ends, from 1 to 

 \ 2 P in length and from 0.1 to 0.5 n broad; short oval and 



j^ %* spherical forms are also frequently observed, and, under 

 98 certain circumstances, longer rods 3 v may be developed : 

 $* / $ 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 

 any evidence that these represent spores. 



This bacillus stains readily with the ordinary aniline 

 colors, but does not retain its color when treated by Gram's 



ciicricii.) . i i 



method. 



Biological Characters. An aerobic (facultative anaerobic), 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 Friedlander'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 size 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 laclis 

 aerogeiies 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 faeces. It resembles the description of the Ba- 

 cillus lactis aerogenes, but the resemblance does not appear sufficient to con- 

 stitute an identity, and, in the absence of a culture 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 see a, and many of the bacilli have the pro- 

 toplasm gathered in the centre, leaving the poles clear. There is some 



