34 



PRACTICAL DAIRY BACTERIOLOGY 



BACTERIUM AEROGENES 



The second type of lactic acid bacterium differs in many re- 

 spects from the first. 1 It is not so common as the first type, 

 but is, nevertheless, very widely distributed, and is very likely 

 to be present in any sample of milk in some quantity. If it is 

 present in large quantities, it becomes a very great nuisance ; 

 if only a few are present, it may do no injury. The organism 

 in question can commojlly be distinguished by a study of the 



,'f\ 





FIG. IQ TYPES OF BACTERIAL GROWTH ON AGAR SLANTS 

 a. Filiform, b. Echinate. c. Beaded. d. Effuse. c. Arborescent 



gelatin plates described on page 288 by the fact that it produces 

 a strongly acid colony which grows on the surface of the gela- 

 tin as a round, more or less raised mass, spreading sometimes 

 to the size of 2 or 3 mm. 



Bact. aero gems, when examined with a microscope, is seen 

 to be an organism somewhat larger than the other lactic type, 

 and one which is, beyond question, a Bacterium, being con- 

 siderably longer than it is broad. Its growth on various 

 laboratory media is very easily distinguished from the first 

 lactic acid type. When inoculated on the surface of agar tubes, 

 or potato, it grows luxuriantly, forming a thick, whitish layer. 

 In gelatin tubes it both grows along the needle inoculation and 



1 Dominikiewicz. Milchztg., p. 817, 1903. 

 Baginsky. Zeit. f. Phy. Chem., xiii., p. 434, 1889. 



