1 68 BACTERIOLOGY. 



balsam. The giant cells are then stained pink, while 

 their nuclei are brown and the bacilli blue (Plate XVII I., 

 Fig. i). 



Bacillus cyanogenus, Fuchs. (Bacterium 

 syncyanum : Bacillus of Blue Milk}. Motile rods 

 2*5 3 '5 ju, in length, and double rods 5*5 6 p. 

 The rods after division may remain linked together, 

 and form chains. Non-motile rods enveloped in a 

 gelatinous capsule, and involution-forms, have also 

 been described. 



Cultivated in a test-tube of nutrient gelatine, the 

 bacilli grow principally upon the free surface, in the 

 form of a white layer. The surface of the gelatine 

 becomes cupped, and a peculiar greenish-brown 

 colour develops in the medium, especially in proxi- 

 mity to the growth. 



On a sloping surface of nutrient agar-agar, it 

 grows as a white layer, and colours the upper part 

 of the medium a smoky brown (Plate II., Fig. 2). 



The bacilli can also be cultivated in milk and on 

 various other substrata, as potatoes (Plate XXI.), 

 boiled rice, and starch. A pure cultivation in 

 sterilised milk develops an alkaline, not an acid 

 reaction. The colouring matter which is formed, 

 varies with the nourishing medium ; for example, in 

 milk a slate-blue coloration is produced, but if the 

 milk has become acid by the growth of the bacillus 

 acidi lactici, then the colour is an intense blue. 



The micro - organism occurs occasionally in 

 cow's milk, producing a blue colour. It has been 



