INFECTIOUS DISEASES AND MICROBES, ETC. 231 



an air-bubble at the top of the track. In the 



following days the gelatine at the top becomes 



liquid, and this liquidity extends gradually to the 



bottom of the track, thus there is a funnel-shaped 



appearance from the greater amount of the fluid at 



the top than at the bottom. At the same time, the 



mass of bacilli falls to the bottom of the fluid and 



assumes a somewhat rosy colour, 



so that there is a rose-coloured 



convoluted string running down 



the lower part of the track. The 



fluid at the upper part, which in 



about a week has extended to the 



sides of the tube, becomes clear, 



except a very thin layer at the 



top, which remains opalescent, 



the top itself being often covered 



with a very fine scum. Scattered 



over the solid gelatine forming 



the sides of the funnel are seen 



numerous small irregular 



refracting particles. These are FlG . 45 . TUBE-CULTIVATION 



the small zooglcea masses which OF CHOLERA-BACILLI. 



. . ,, ^ . , , (After Watson Cheyne.) 



have fallen to the sides and 

 bottom of the funnel-shaped cavity (Fig. 45), and 

 which Dr. Watson Cheyne considers the most typi- 

 cal appearance during the growth of the comma 

 bacillus in tube cultivations. On agar-agar the 

 comma bacillus grows fairly well, but it does not 

 liquefy this medium. On blood serum (at 37 C.) 

 this microbe grows most luxuriantly. It also grows 

 in milk, but gives rise to no noticeable alterations ; 



