FIRE-BLIGHT OF APPLE, PEAR, ETC. I CAUSE 



371 



stimulates growth, as Waite supposed. Test. Unneutralized 

 acids of gelatin inhibit growth. Tests may be made. Growth 

 is best when the gelatin is made neutral or nearly neutral 

 to phenolphthalein by use of sodium hydrate. Acids are 

 formed from various sugars. In Uschinsky's solution no 

 growth, or slow growth, unless peptone is added: growth copi- 

 ous, not viscid (D. H. Jones). In Cohn's solution no r ;growth 

 or slight (Repeated in 1915 with the same result). The opti- 

 mum temperature is 30C. Growth at 3C. is very slow 

 (D. H. Jones), and there is no growth at 0.5C. Exposure in 



FIG. 286. Cross-section of a young pear shoot showing cavities in the bark 

 due to Bacillus amylovorus. The bacteria diffuse out of such cavities very readily 

 on staining. Inoculated by the writer in May, 1915. 



beef broth at 43C. for 10 minutes retards growth and at 43.7C. 

 kills (L. R. Jones). The thermal death point in bouillon lies 

 between 45 and 50C. (D. H. Jones). In liquids all are killed 

 by ten minutes' exposure to 55C. (O'Gara). In a recent 

 inoculation (Oct., 1919) using our 1915 isolation from apple, the 

 organism clouded at 43C. (but with retardation) and finally 

 at 44C. One also of the four tubes exposed at 45C. clouded 

 (after 6 days) but none at 48C. (15 days), when exposed 

 for 10 minutes in the water bath in +15 peptone beef bouillon. 

 The checks grew promptly and the six uninoculated tubes re- 



