On Plant Pathology and Ba(;tl:iuology 117 



" that I had confounded in my published accounts a non-patho- 

 genic with the true pear bhght bacillus, but that chieily affected 

 the morphological part of my work. What you have said of my 

 work is certainly true, and could not have been better stated by 

 myself." Smith had written: "'' 



Dr. Arthur repeated Prof. Biirrill's experiments and carried tlie work 

 considerably farther. In 188-4, at the Geneva Experiment Station, in New 

 York, he made 121 inoculations into . . . pear, apple, quince, hawthorn, 

 June-berry, mountain ash, blackberry, peach, grape, etc. The infectious 

 material was obtained 'from freshly blii^hted twigs and fruits and con- 

 sisted at first of the extruded gum, and subsequently and in most cases of 

 drops of water which had been rendered slightly milky by cutting it into 

 sections of freshly blighted twigs swarming with the bacteria, the milki- 

 ness being due to the enormous number of bacteria held in suspension. 

 These inoculations were made in the station orchard under peculi;:rly 

 favorable circumstances, there being an abundance of material of all sorts 

 for experiment and scarcely any natural blight nearer than a mile and a 

 half. On the Station farm the only occurrence of blight on uninoculated 

 trees was confined to a few twigs of one of the quince trees and to a few 

 branches on a pear tree a half mile distant, which twigs and branches 

 were cut out promptly. Under these circumstances Dr. Arthur obtained 

 53 successful infections, the first symptoms appearing usually in 3 to 8 

 days, but sometimes in less favorable tissues not until after 10 to 23 days. 

 The failures were due to inoculations into too old tissues (old stems, leaves 

 and fruits), to unfavorable weather conditions, and to inoculations into 

 non-susceptible plants — peach, grape etc. ... At this time it was still 

 believed by many scientific men that infectious diseases were due primarily 

 to chemical substances and not to the bacteria which were associated with 

 the diseases. With this in mind. Dr. Arthur on six different occasions 

 separated the juice of blighted tissues from the bacteria by filtration 

 through unglazed baked clay cups. In every instance the filtered fluid 

 failed to produce the disease when inoculated into susceptible tissues. In 

 every case the same tissues blighted promptly when inoculated with a tiny 

 quantity of the bacterial residue. Subsequently he made pure cultures or 

 what he supposed to be such, and which probably were such, by inoculat- 

 ing tubes of sterile corn meal broth with bacteria from the interior of 

 freshly blighted tissues. When well clouded, a drop from one of these 

 tubes was transferred to another tube and so on through six tubes. Under 

 careful control conditions pear blight was twice produced from such 

 cultures. 



In 1886 Arthur discussed ^"^ "preventives and remedies" for 



"^ Cent. f. Bakt. II, 5 (23): 812-813, 1899; 5 (8): 276-277. 

 ^""J. C. Arthur, Pear blight, Rep't of the Myc. Sect., Rep't of the Comm'er of 

 Agric. for 1886: 125-129. 



