GENUS BACTERIUM 299 



A FEW SPECIES OF THE GENUS BACTERIUM WHICH ARE 

 COMMONLY NOT PATHOGENIC. 



BACTERIUM AEROGENES (ESCHERICH) MIGULA. 



Synonyms. Bacterium lactis aerogenes Escherich x ; Bac- 

 terium lacticum Babinsky ; Bacillus aerogenes Kruse. 



Place in nature. This is the type of a group of bacteria 

 which are closely related in their biological properties to B. 

 coli but quite distinct from it. It was discovered by Escherich 

 in 1885 in the feces of infants. It is widely distributed in 

 nature, being found in water and in sewage. It is a common 

 cause of souring in milk. 



Morphology. Bad. aerogenes is about 0.5 to 1.0 /x in 

 width and from 1 to 2 /A in length. It has rounded ends. It 

 rarely appears in chains except in milk where it is more com- 

 mon. When cultivated on suitable media, especially milk, a 

 capsule is in evidence. It does not produce spores. 



Staining. It stains \^ith ordinary aniline dyes but it is 

 Gram negative. 



Cultivation. It is cultivated on the usual media without 

 difficulty. 



Agar. Upon this medium it develops a heavy white 

 growth. The colonies when isolated have a tendency to con- 

 fluence and are distinctly morejnucpid in appearance than 

 are those of Bacillus coli. 



Gelatin. The growth on gelatin is quite vigorous. The 

 medium is not liquefied. 



Potato. The growth is heavy and gas is formed. 



Bouillon. In bouillon, it causes a general clouding and 

 a pellicle. The cultures have a slightly sour or cheesy odor. 

 It ferments dextrose and lactose with the formation of gas. 

 In the fermentation of dextrose there is 50 per cent gas 

 CO 2 35, H 65. With lactose it is 62 per cent gas C0 2 38.5 and 

 H 61.5. According to Smith 2 saccharose is not attacked. 



1 Escherich. Die Darmbakterien des Sauglings, 1886, p. 57. 

 Fortschritte d. Medizin, Bd. Ill (1885) p. 237 and p. 515. 



2 Smith. The Wilder Quarter-Century Book, 1893, p. 209. 



