336 PROCEEDINaS OF THE ACADEMY OP [1886. 



germs wei'e well distributed by shaking and then left undis- 

 turbed for two days, gave the same isolated white dots as in 

 gelatine; but they dropped to the bottom of the liquid upon 

 being jarred. The bacteria were evidently prevented from 

 moving freely by the jelly, which was not, however, thick 

 enough to keep the groups in place when its cohesion was 

 once disturbed. Fruit jellies, doubtless, may be found to be 

 convenient media for the cultivation of this species of bac- 

 teria. 



No success has been attained in the use of agar agar, but 

 whether due to a want of adaptability in the substance, or to 

 wrong manipulation, must be left to future experiments to 

 determine. 



The opaque solid cultures proving most successful have been 

 conducted upon freshly gathered unripe pears. Slices of these 

 are placed under a moist bell-jar, and infected by touching with 

 a needle that has been dipped in some substance containing the 

 bacteria. In two or three days fine milk}^ drops, like beads of 

 dew, will appear scattered over the surface for 5 mm. or more 

 about the infected spot. These will become somewhat lai-ger 

 after a time, while the spot which received the infection will turn 

 slightly brown, the tissues gradually wasting away and forming 

 a small depression. 



If, however, the slices, having freshly cut surfaces both above 

 and below, are laid upon a plate with a little water, and placed 

 under a bell-jar, the result is not the same. The dew-like drops 

 appear within forty-eight hours, as in the other case, but increase 

 rapidly in size, while a drop is also formed at the point of infec- 

 tion. Drops finally appear over the whole surface of the slice. 

 They remain more or less distinct, and soon become as large as 

 a pea, retaining the globular or rounded form to a remarkable 

 degree. Microscopically the}'^ ai-e composed of the usual form 

 of blight bacteria, suspended in a colorless fluid. After about a 

 week, the drops coalesce and the tissues of the pear begin to 

 break down. This sort of culture requires no precautions of 

 sterilizing, as no other bacteria can multiply upon it till after the 

 cells of the pear begin to die. 



When blight bacteria are sown upon slices of baked or boiled 

 potato, they spread out over the surface in a thin, slightly moist 

 layerj which is usually somewhat yellowish, but do not grow 



