38 



THE GUMMOSIS OF THE SUGAR-CANE, 



The Conditions of Gum-Formation. 



Having proved the relationship of the gum to the bacterium, 

 there remained the determination of the conditions under which 

 the gum is formed. The slime had been first obtained in 

 quantity by growing the bacteria upon cane-juice agar, i.e., a 

 solution of 4% of agar added to an equal volume of neutralised 

 cane-juice; and although the growth was very good, yet there 

 appeared to be room for improvement. The best medium is 

 undoubtedly very faintly acid cane-juice gelatine, but, unfor- 

 tunately, this cannot be employed when the slime is wanted for 

 chemical investigation, because the medium is slowh^ liquefied. 

 The first experiment was made upon cane-juice agar, and had for 

 its object the question of the improvement of the agar by peptone 

 and, incidentally, the eflfect of a temperature of 30° as against 

 22° C. Previous tests had shown that no growth occurred at 

 37°. In this and the following experiments the numbers 

 indicate the order of merit of the cultures at the time of observa- 

 tion ; 1 being the most luxuriant growth, 2 the next best, and 

 so on. 

 The Effect of 1% Peptone on Cane-agak Cultures at 22"^ and 30° C. 



This experiment showed that more slime was formed when the 

 cane-agar contained 1% of peptone, and when the culture was 

 incubated at 30°. There, however, is the doubt that 1% peptone 

 is too much, and to test this point various quantities of a 10% 

 peptone solution were added to 10 c.c. portions of a faintl}^ acid 

 medium containing glucose 10%, sodium phosphate 0-2%, 

 potassium chloride 0-5%, agar 2%, and the bacteria were inocu- 

 lated upon the sloped surface of the portions. Cane-agar was not 

 used on account of the unknown nature of the constituents. 



