292 



BACTERIA IN RELATION TO PLANT DISEASES. 



The optimum reaction for growth in peptonized beef-bouillon is about +8 of Fuller's 

 scale. Growth on the acid side (acid of beef-juice) takes place up to about +28 (?) ; on the 

 alkaline side (sodium hydrate) growth ceases at about 4 (?). These statements are to be 

 taken only as general indications, for here again much depends on the original reaction of 

 the culture-fluid used for the inoculation. Growth may be pushed farthest on the acid side 

 by inoculating from acid bouillons, and on the alkaline side by inoculating from alkaline 

 bouillons, e. g. 2 bouillon will cloud when inoculated from + 2 or o bouillon, but not when 



inoculated from +25 or +20 bouillon. The 

 strain used for these experiments was the 

 one which did not infect squash (1905). 



In milk, growth continues for quite a 

 long time but with no precipitation of casein 

 or change in the appearance of the fluid. In 

 litmus-milk there is little or no change of 

 color, i. c, no decided reddening or bluing 

 of the fluid, or loss of color (reduction) not 

 even after several months. It has seemed 

 to me at times that I could distinguish a 

 slight change in the color of the litmus-milk 

 (bluing), but if any it is so slight as to be 

 readily overlooked. Milk is, therefore, a 

 good differential culture-medium. In old 

 litmus-milk-cultures (dried out two-thirds), 

 on the walls of the tubes above the fluid, 

 very small branching fern-like crystals (fig. 

 96) occurred after wetting the walls with 

 the fluid, and these crystals did not appear 

 in the 3 check tubes. On litmus-lactose-agar 

 there is no change at first. After some time 

 there may be a gradual deepening of the 

 blue color, but never any reddening. This 

 experiment was repeated in 1906 with the 

 same result. 



Only one bacillus more sensitive to dry 

 air is yet known, viz., B. carotovorus Jones. 

 In the writers' experiments, portions of solid 

 cultures or fluid cultures were spread in thin 

 layers and dried at room-temperatures on 

 clean sterile cover-glasses and then tested 

 by dropping from time to time into tubes of 

 a bouillon known to be well adapted to the 

 growth of the organism. In all cases the 

 organism was found to be dead one-half 

 hour to one hour after dryingout,andinsome 

 instances when taken from bouillon drying for so short a time as 15 minutes sufficed to kill 

 it. Covers inoculated from the same bouillon and dried only for 10 minutes yielded cultures 

 of the organism when thrown into bouillon. Much seemed to depend on the thinness of 

 the layer. Possibly also the surface on which the bacillus is dried may exert an influence. 

 The bacillus is also sensitive to sunlight (fig. 97.) 



*Fig. 91. o, streak culture of Bacillus tracheiphUus on litmus-lactose agar after 7 days, showing frequent tend- 

 ency of organism to grow in discrete colonies. Tube 15, June 30, 1904. Photographed July 7. Xi H- b, Same 8 days 

 old at 22 to 26C. In this tube it is also growing in the form of a streak. Tube 4, June 16, 1903. Photographed, 

 June 22. X2. 



Fig. 91. 



