32 Bacterial Disease of the Mango 



light salmon orange (II), and the upper half peach red (1). After three 

 days the upper third of the tube only retained any colour and in five 

 days it was colourless. The only considerable variation in this process 

 was in the length of time which it occupied ; the medium in every case 

 became slightly acid and then bleached out from the bottom upwards. 



Neutral red. Tubes of nutrient broth tinted carmine (I) with this 

 stain were inoculated and incubated at 30° C. The organism grew 

 well in this medium, and a fairly heavy ring formed round the tube at 

 the surface of the liquid. The cultures were kept under observation 

 for ten days, but no reduction took place. The bacterial ring absorbed 

 the colouring matter and became carmine. Rods from this ring when 

 mounted in water and examined microscopically were faintly stained ; 

 there were some short capsuled rods, and some long filaments of rather 

 uneven breadth similar to those found in media containing Nad. 



Rosolic acid. The colour of the medium at the beginning of the 

 experiment was peach red (I). After 24 hours at 30° C. the colour was 

 bittersweet orange (II), and it subsequently passed through buff (III) 

 to light orange yellow (II). In six days the culture was entirely colour- 

 less except for the bacterial ring at the surface of the liquid which had 

 absorbed the colouring matter and become orange red. The stain was 

 not in this case sufficiently intense to be evident in the bacilli when they 

 were examined microscopically. 



Methylene blue. A number of tubes and fermentation tubes were 

 prepared containing broth tinted with methylene blue to the colour of 

 a strong ammoniacal solution of copper sulphate. The closed arm of 

 the fermentation tube was colourless after sterilisation and remained 

 so throughout the experiment; the description of changes of colour 

 therefore refers to the ordinary test tubes, and to the open arm of the 

 fermentation tubes. 



As in the case of tubes coloured with litmus solution reduction 

 commenced at the bottom of the tubes. After the cultures had been 

 kept at 30° C. for 24 hours the lower part of the tube was colourless and 

 the upper part Tyrolite green (VII). On the second day there was only 

 about -| cm. at the surface of the liquid which retained the green colour. 

 After six days the medium was colourless, but the bacterial ring had 

 partially absorbed the colour and was Venice green (VII). 



The colour did not return at all when the tubes were shaken. 



Indigo carmine. Indigo carmine was also gradually reduced from 

 the bottom of the tube upwards. In this case the organism did not 

 absorb the colouring matter. Reduction was complete in eight days. 



