COBB'S DISEASE OF SUGAR-CANE. 63 



elements necessary for growth, *'. e., nitrogen or some other substance may have been lack- 

 ing; or (4) the enzyme presumably present in the gum may have been destroyed in some 

 inadvertent way or rendered inactive. All it proves beyond question is that the "gum" 

 did not act on the cane-sugar under the conditions of the experiment. Boname's analyses 

 show that diseased canes have a smaller sugar-content than sound ones, and so do those 

 cited from Cobb's paper. Some analyses made by Miiller and published by Tryon show 

 only about i per cent difference between gummed cane and cane supposed to be free from 

 gum, but this i per cent is on the side of the healthy cane. 



Growth is not inhibited by sodium chloride in small quantities, e. g., there is feeble 

 growth in peptone water with 0.5 per cent and i per cent NaCl, but larger amounts (1.5 per 

 cent, 2 per cent, and 2.5 per cent) prevent growth. Greig Smith also found that 2.5 per 

 cent sodium chloride was a distinct poison. In cultures in i per cent peptone-water with 

 o.i per cent oxalic acid there is no clouding of the fluid, but a finely granular and flaky or 

 stringy precipitate is formed. 



The following acid agars gave negative results: Beef-agar with 0.2 per cent oxalic acid 

 (1687) ; beef-agar with o.i per cent malic acid (1682) ; 2 per cent beef-agar with 0.2 per cent 

 oxalic acid (1776) ; 2 per cent beef-agar with 0.2 per cent citric acid (1777) ; 2 per cent beef- 

 agar with 0.2 per cent malic acid (1787). There was no growth whatever on any of these 

 agars. 



Greig Smith reports the following results of experiments made to determine the reaction 

 of the medium best suited to the bacterium. The medium used was water containing 0.5 per 

 cent peptone, 5 per cent saccharose, 0.5 per cent [di ?] potassium phosphate and 2 per cent 

 agar, to which were added various quantities (o.oi per cent, 0.02 per cent, 0.03 per cent, 

 0.05 per cent, 0.08 per cent) of solutions containing 10 per cent tartaric acid and 10 per cent 

 sodium carbonate. He says: 



The effect of slight differences of acid or of alkali in the culture media is very pronounced. In an 

 absolutely neutral medium [neutral to what?] the bacteria grow very slowly, while, when the reaction 

 is faintly acid, the growth is quick and luxurious. Alkalies prohibit the multiplication of the microbe. 

 With 0.02 per cent the stroke was slow to show itself, was always scanty, and finally, after ten days' 

 incubation, it dried up. 



A series of experiments made for me by John R. Johnston to determine from what com- 

 pounds the organism could obtain its nitrogen and carbon resulted as follows: 



Nitrogen-free medium (1664*) with 0.5 p. ct. asparagin. Well clouded with thin film on the surface. 



Nitrogen free (1664) with 0.5 p. ct. sodium asparaginate. Moderately clouded; a slightly yellowish more or less gran- 

 ular film on surface. 



Nitrogen-free (1664) with 0.5 p. ct. ammonium citrate. Heavy flocculent clouding, heavy precipitate. 



Nitrogen-free (1664) with 0.5 p. ct. ammonium lactate. Moderately clouded. 



Nitrogen-free (1664) with 0.5 p. ct. ammonium tartrate. Moderately clouded. 



Fischer's mineral solution (nitrogen-free). f Very slight growth. 



Fischer's mineral solution with i p. ct. cane-sugar. Very slight growth. 



Fischer's mineral solution with i p. ct. KNO t . Very slight growth. 



Fischer's mineral solution with i p. ct. KNOi and i p. ct. cane-sugar. Very slight growth. 



Fischer's mineral solution with i p. ct. KNOi and I p. ct. dextrose. Very slight growth. 



Fischer's mineral solution with i p. ct. Witte's peptone. Thinly clouded; small precipitate. 



Fischer's mineral solution with i p. ct. Witte's peptone and i p. ct. dextrose. Moderate clouding; small, yellow pre- 

 cipitate. 



Fischer's mineral solution with i p. ct. Witte's peptone and i p. ct. glycerin. Moderate clouding. 



Fischer's mineral solution with i p. ct. Witte's peptone and i p. ct. cane-sugar. Heavily clouded; yellow precipitate, 

 white surface pseudozoogloeie. 



Fischer's mineral solution with I p. ct. asparagin and i p. ct. dextrose. Good growth. 



Fischer's mineral solution with i p. ct. ammonium tartrate and I p. ct. dextrose. No growth. 



Water with 2 p. ct. asparagin and I p. ct. dextrose. Thinly clouded, growth much retarded. 



Water with 1.2 p. ct. asparagin and i p. ct. Witte's peptone. Well clouded, blackish (?) precipitate. 



Stock 1664: fFischer's mineral solution: 



Cane-sugar 9.00 Dipotassium phosphate a.o 



Dipotassium phosphate 9.00 Magnesium sulphate 0.4 



Magnesium sulphate 0.90 Calcium chloride o.a 



Sodium chloride i .80 Distilled water 2,000.0 



Calcium chloride 0.45 



Distilled water 1,800.00 



