FERMENTED MILKS. 21 



undoubtedly nearly or quite identical and all are included under the 

 name Bacillus bulgaricus, now generally adopted. More strict ad- 

 herence to the commonly accepted rules of bacteriological nomen- 

 clature would retain the name Bacterium caucasicum proposed by 

 Beyerinck. Eecent work by Hastings (32) and by Heinemann and 

 Hefferan (36) indicates that this bacterium is not peculiar to the 

 eastern fermented milks, but is widely distributed, having been iso- 

 lated from milk, soil, saliva, feces, and various soured foods. White 

 and Avery (82) believe that this bacterium is the representative of 

 a group of closely related bacteria which they divide into two types 

 on the basis or" their activity in milk and the nature of the lactic 

 acid formed. The characteristics of the typical culture may be sum- 

 marized as follows: 



Morphology. — Slender rods 2 microns to 6 or 8 microns in length, 

 breadth usually about 1 micron, flagella and spores absent. Long 

 chains frequently occur and apparently vary with different strains 

 and conditions; pseudobranching has been observed. Very long 

 threads without apparent division are frequently observed in old 

 cultures. Living cells are gram positive; dead cells are gram nega- 

 tive. 



Growth on artificial media. — One of the most striking features is 

 its inability to grow on ordinary media. It grows on whey, malt, 

 and slowly on whey agar and certain specially prepared media. The 

 colonies on whey agar are masses of tangled threads resembling colo- 

 nies of the anthrax bacillus. Gelatin is not liquefied. 



Relation to oxygen. — Most varieties grow equally well in the pres- 

 ence or absence of oxygen. 



Temperature relations. — The maximum temperature is near 45° C. 

 (113° F.). The minimum growth temperature varies with different 

 members of the group, but it is always comparatively high. Most 

 varieties grow very slowly at 25° C. (77° F.), but some grow at 

 20° C. (68° F.). Hastings and Hammer (33) state that at 20° C. 

 (68° F.) it forms 4 per cent acid in milk as compared with a maxi- 

 mum of 3 per cent at 37° C. (98° F.). According to White and 

 Avery (82) it is killed by an exposure of 15 minutes at 60° C. 

 (140° F.). 



Fermentation of sugars. — Many of the sugars are fermented, but 

 statements of different workers are conflicting. It is probable that 

 this property varies in different varieties. 



Milk. — The action of this organism on milk distinguishes it from 

 all other known bacteria. At the optimum temperature milk is 

 curdled in a few hours with a rather soft curd, frequently somewhat 

 slimy, which ordinarily docs not separate from the whey even on 

 Umg Standing, In 21 hours the milk may show acidity equivalent to 



