24 Studies in Bacteriosis 



The question of auto-intoxication of the bacteria was next con- 

 sidered. A broth culture of the organism was placed out in uniform 

 drops upon small squares of sterile mica and maintained in a moist 

 Petri dish. Periodical counts of the organisms were made in bouillon 

 agar after suitable dilution in sterile water. The numbers of living 

 bacteria remained about 3-4 millions for five weeks (disregarding one 

 low count of 1,760,000) and at the end of eight weeks, when the experi- 

 ment was concluded, they still amounted to nearly one million. The 

 falling off of the numbers in the infection experiments, which became 

 marked in 30 days and 40 days in July and October respectively, was 

 therefore not due to auto-intoxication of the invading organism. 



The resistance of the organism to desiccation was next investigated. 

 Two measured drops of a broth culture were placed on squares of sterile 

 mica. One was immediately washed off with sterile water and plated. 

 The number of organisms present was determined as 1,328,000. The 

 other drop was allowed to dry for 24 hours and was then washed and 

 rubbed off the mica with a sterile glass rod. The numbers of bacteria 

 were found to have fallen to 11,000. In a second experiment the num- 

 bers were reduced from 890,000 to 15,000 in 24 hours, to 6400 in four 

 days and to zero in eight days. 



In order to approach more nearly the conditions of nature the 

 experiment was repeated using in the place of the mica small pieces of 

 Pratea leaf which had been dried in air after having been heated in the 

 autoclave. A water suspension containing some four million organisms 

 per drop was employed and the result was as follows: after 1 day, 

 2,044,340; 2 days, 569,050; 3 days, 7069; 6 days, 7214; 9 days, 802; 

 13 days, 320. 



Obviously desiccation is an important factor and no doubt accounts 

 for the death of the organism in the diseased tissue. The non-viability 

 in the dry gum and viability in moist gum as described on p. 22, is 

 explained in this way, as also is the relatively slower onset of sterility 

 in the October infection experiment as compared with the July experi- 

 ment described above, drying presumably being more rapid in July. 



Under favourable conditions the moisture content of the invaded 

 tissue remains sufficiently high to maintain the life of the organism for 

 some considerable time. The organism has been re-isolated from arti- 

 ficially infected spots 65 and 75 days after infection. Even after the 

 lapse of 16 weeks in one case two colonies of P. Proteamaculans were 

 obtained on grinding the diseased spot and plating. 



The rapid growth of the organism and the area of the spots produced 



