BITTER MILK 283 



strated by Fuchs in 1841. The colour is due to the 

 activity of a bacterium named 



Bacillus lactis cyanogenes, by Hiippe (Bact. syncyaneum^ 

 L & N.), a motile aerobic rod-shaped form i to 3 /a long and .5 // 

 thick. After introduction into fresh milk it induces a blue 

 colour in from one to three days, or earlier if the temperature is 

 maintained at about 20 C. The colour appears first at the 

 surface of the milk in small spots or patches, and spreads slowly 

 into the deeper parts. The production of a rich deep blue tint 

 is dependent upon the simultaneous production of a certain 

 amount of acid by the lactic organisms, although the acid is 

 removed in some way almost as fast as it is formed, since the 

 coloured milk has an alkaline reaction. On keeping, the colour 

 changes to a dirty grey or brown. The colonies on gelatine are 

 usually yellowish- or greyish- white at first, but later become brownish 

 purple. It is easily checked by the presence of other bacteria, 

 and is destroyed at a temperature of 60 or 70 C. A greyish 

 tinge only is developed by the bliie milk bacillus in sterilized 

 milk or in fresh milk which has not become acid. 



Ex. 138. Prepare stained slides of the following organisms : 



Bact. lactis viscosus, Adamtz. 

 Str. hollandicus, Sch. 

 Micrococcus rose us, L. & N. 

 Bs. prodigies-its, Fliigge. 

 Bs. lactis cyanogenes, Fliigge. 



a. Examine with high power, and make drawings of each. 



b. Try their action upon (i) fresh milk, and (2) milk to which 



sugar has been added. 



c. Grow them upon gelatine and agar media, and note the 



form and colour of the colonies. 



4. Bitter Milk. The bitter flavour of milk some- 

 times appears to be brought about through the con- 

 sumption by the cows of leaves of turnips and other 

 cruciferous plants, lupins, and vetches, as well as certain 



. 



