34 Stndies in Bacteriosh 



different cultures of the organism. The inoculations were made in various 

 ways, and of the fourteen attempts only one failed to produce infection. 



Experiment 1. May 29th, 1918. The surface of a leaf of a potted 

 plant was sterilised by washin<i with alcohol and two inoculations were 

 made by placing a spot of slime from an agar culture (the third transfer 

 from the original isolation) upon the upper surface of the leaf and 

 pricking through this into the leaf with a flamed needle; two controls 

 were made by similarly pricking through slime which had been heated. 

 May 31st: a translucent margin one millimetre wide had appeared round 

 the punctures, and a mucilaginous drop was present above the point of 

 infection; control spots had dried up. June 2nd: tissue was brown in a 

 zone of 2 mm. radius round the prick ; control pricks were dry and 

 browned only at the edge of the needle puncture. June 8th: typically 

 diseased spots; controls dried out. Plate cultures from a suspension of 

 the diseased tissue showed on June 10th development of many colonies 

 of two distinct types with a strong preponderance of that characteristic 

 of the disease organism. A second plating from these gave pure cultures 

 which were used in Experiment 3. 



Experiment 3. June 12th, 1918. The organism re-isolated from the 

 leaf of Experiment 1 was pricked into a cut leaf placed on moist blotting- 

 paper in a Petri dish and kept at room temperature. June 17th: tissue 

 was brown and typically diseased two millimetres round both infection 

 spots and mucilaginous drops were standing above as in Experiment 1 ; 

 control pricks had dried up. A suspension of the diseased tissue was 

 employed in Experiment 7. 



Experiment 7. June 18th, 1918. Diseased tissue from leaf of Experi- 

 ment 3 was suspended in sterile water and pricked into a leaf of a growing 

 plant. June 30th: all inoculated spots were typically diseased; all con- 

 trols had dried up. 



Experiment 4. June 14th, 1918. The organism from an agar slope 

 (the fifth transfer from the original) was pricked into a cut leaf with its 

 petiole immersed in sterile water and covered with a bell-jar. It was 

 placed in strong light in the greenhouse laboratory. June 20th: around 

 the two infection pricks the tissue was browned in a spot 4 mm. diameter 

 and this was surrounded by a wider zone 6 or 7 mm. diameter in which 

 the bright vermilion pigment typical of the disease in young leaves had 

 developed abundantly. A photograph of this leaf appears in Plate II, 

 Fig. 2. 



Other infections were obtained by hypodermic injection of pure 

 cultures, by placing bacterial slime upon the leaf surface without punc- 



