Sydney G. Paine and Emily M. Berridge 



•23 



were made in bouillon agar and the colonies counted after two days 

 incubation^. Fig. 1 shows the result of this experiment. It will be seen 

 that the numbers rose from 1,242,000 on the sixth day to 2,808,000 on 

 the fifteenth day, and then fell rapidly to 16,000 on the thirty-second 

 day, when the experiment came to an end. This experiment was made in 

 July. A repetition was made in October of the same year, drops of a 

 suspension of the organism in sterile water being used instead of a bouil- 

 lon culture. This series was very unsatisfactory in the number of success- 

 ful inoculations; out of 24 spots only the following five records were 



Days 5 10 15 20 25 30 



Fig. 1. Showing the rise and fall in the numbers of bacteria in leaf spots artificially 

 infected with Pseudomonas Proteamaculanx. 



obtained: after 9 days, 1,280,000; 15 days, 1,576,000; 27 days, 1,808,000; 

 35 days, 1,336,000; 40 days, 485,000. 



A sixth spot showed an exuded drop of mucilage which has been 

 regarded as the first sign of active infection only on the forty-third day 

 and gave a count of 1,850,000. A seventh spot developed actively some 

 time later. 



These experiments showed clearly that the rate of destruction of the 

 organism was not very rapid, and again negatived the hypothesis of the 

 production of a bacteriolysin by the invaded cells. 



^ The degree of accuracy of this method was tested in the following maimer : First, as 

 to the uniformity of the individual drops of bacterial suspension appUed to the leaf — nine 

 drops were plated separately and counts made after two days' incubation varied from GOl 

 to 746. Second, as to the number of bacteria lost by adsorption on the sand and ground-up 

 tissue — four experiments were made comparing the numbers in drops of suspension before 

 and after grinding with sand and sterile leaf tissue : in one of these the loss was 20 per 

 cent, and in the other three 9 per cent. 



