H. WORMALD 237 



the fifth being kept as control and for comparison. 24 hours after 

 inoculation each tube showed a slight reddening of the litmus (com- 

 pared with the uninoculated) and a dense sediment was beginning 

 to accumulate in the basal part of the tubes. After another period 

 of 24 hours the red colour was more intense and there was a copious 

 sediment while the liquid itself was more transparent^. Within six 

 days the liquid above the sediment was clear and almost colourless. 

 Later the contents of the fermentation tubes were filtered ; the filtrate 

 was clear and colourless, the sediment remaining on the filter. That 

 portion of the original culture medium still remaining in the uninoculated 

 tube passed through the filter unchanged, leaving behind no sediment. 

 A solution in which pectin was the only source of carbon was also 

 used and prepared as follows : — 



This, when sterilized, was found to give a distinct acid reaction 

 and the organism made but slight development in it. On neutralizing 

 the medium with a solution of NaOH inoculated tubes became turbid 

 in 24 hours and a distinct sediment was present after four days; on 

 testing with litmus the tubes gave a pronounced acid reaction not 

 shown by controls. 



Pectin therefore may be substituted for sugar in the preparation 

 of culture media for the celery-rot organism and probably also for other 

 soft-rot bacilli; since pectic compounds are readily attacked by these 

 forms and as this ability to render soluble the middle lamellae of the 

 tissues is the primary cause of the damage done to succulent organs of 

 many garden and field crops, such culture media might yield interesting 

 results relative to the mode of parasitism of soft-rot bacteria. 



Uschinsky's Solution. Growth in this medium is vigorous, turbidity 

 being evident within 24 hours of inoculation; flocculi then appear 

 together with some sediment during the second day. After a few 

 more days the medium becomes almost clear again and there is a bulky 

 sediment which eventually forms a dense glairy mass at the bottom of 



1 Owing to the concentration of the pectin the medium before inoculation is only 

 semi-transparent. 



16—2 



