3O PRACTICAL DAIRY BACTERIOLOGY 



distinctive feature of which is the rather dense red colony, 

 with a series of very slight projections around the edge, so that 

 the colony looks almost burr-like. These 

 projections are very short and not al- 

 ways found; but when they are found, 

 it is practically certain that the colony 

 represents the Bact. lactis acidi. It 

 should also be borne in mind that no 

 bacterium that grows on the surface 



FIG. .6-COLON,ES OF Q{ ^ ^ Q{ ^ fo| . ^ 



BACT. LACTIS ACIDI 



IN LJTMUS GELATIN organism grows only under the sur- 

 face. 



^Characteristics of Bact. Lactis Acidi. This organism is of 

 so much importance to dairymen that it is necessary to study 

 it in more detail, and the following description of the growth 

 of this organism and the various culture media used in the 

 laboratory will serve to identify this type. Its growth on the 

 surface of any culture medium is extremely scanty. No growth 

 can be seen on potato, and none on the surface of gelatin 

 plates. When inoculated on agar slants there is an extremely 

 thin growth, almost invisible, although it may be seen, by very 

 careful examination, as a clear, transparent film. On the other 

 hand, it grows fairly well in the depth of culture media away 

 from contact with air. Inoculated by a needle, into a gelatin 

 tube, it grows well below the surface along the line of inocula- 

 tion (Fig. 17), but it stops at the surface and never spreads 

 over it. When inoculated into ordinary bouillon, usually no 

 visible signs of growth are seen, although the organism does 

 grow slightly. Inoculated into fermentation tubes containing 

 bouillon with milk sugar or dextrose, there is always a scanty 

 growth giving rise to slight turbidity, and growth may extend 

 up the closed arm of the tube, as well as in the open arm, in- 

 dicating that the organism grows without contact with oxygen 

 (Facultative anaerobic) . 



