TYl'KS OF BACTERIA FOUND IX MILK 



35 



spreads over the surface. (Fig. 19, 6.) In bouillon it grows 

 luxuriantly, producing a turbidity and sediment. Inoculated 

 into fermentation tubes containing sugar, it grows both in the 

 open and closed arm, and in all cases produces gas which 

 collects at the top of the closed arm. (Fig. 20.) This lat- 

 ter is the most important character of 

 this type. When inoculated into milk, 

 it causes the souring of the milk, which 

 is rapidly followed by curdling, the 

 rapidity of the curdling varying in dif- 

 ferent specimeri3. -The curd which is 

 produced differs very much from that of 

 the first type of lactic acid bacteria. It 

 is always more or less filled with gas 

 bubbles, and when care is taken to ob- 

 tain a typical curd, it appears, as shown 

 in figure 18, A, crowded with holes 

 which represent the bubbles of gas 

 formed by the organism. The whey 

 commonly separates in a short time from 

 the curd, and the final appearance is 

 strikingly different from that of the 

 curdled milk produced by the first type 

 of lactic acid bacterium. There is also 



,. . FIG. 20 PRODUCTION OF 



a difference in the type of lactic acid GAS IH FERMENTATION 

 produced by the two organisms, the first TUBE, PRODUCED BY BACT. 



LACTIS AEROGENES 



producing what chemists refer to as 



right-handed lactic acid, and the second producing chiefly left- 

 handed acid, two terms referring to the effect of the acid upon 

 polarized light. 1 



This organism plays a great deal of mischief in dairying. 



1 Utz. Cent. f. Bact. II., xi., p. 600, 1904. 

 Thiele. Zeit. f. Hyg., xlvi., p. 395, 1904. 

 Heinemann. Jour. Biol. Chem., II., p. 603, 1907. 



