1902.] 



Pseudomonas destructans (Potter). 



393 



and formed an irregular bag in the centre of the cell. This contrac- 

 tion was not due to mere plasmolysis, but to the death of the cell 

 under the action of the toxin, as the protoplasm never returned to its 

 original position when placed in water. 



Thus, within an hour and a-half of the introduction of the Pseudo- 

 monas, the cell was dead and its walls well advanced in a process of 

 disintegration. After this the changes were less rapid, and, beyond a 

 slight further separation of the cells, a more watery and rotten appear- 

 ance of the cell-wall was all that could be observed. 



Meanwhile the adjacent cells at the edge of the section were all 

 being attacked in a precisely similar manner ; contraction of the pro- 

 toplasm set in at 11.30, and the decay could be observed gradually 

 spreading inwards. 



The original cell was kept under observation for some days and the 

 development watched. The bacteria continued swarming around the 

 cell- walls, and next morning (by which time the cells had been 

 destroyed several layers deep) many bacteria had come to rest in 

 contact with the wall, their long axis being perpendicular to its 

 surface ; and one or two had the appearance of being embedded in the 

 wall as if in the act of boring their way through. I next attempted 

 to watch a single individual in the hope of seeing it penetrate the 

 wall ; this at first seemed rather a hopeless task, but ultimately I was 

 fortunate in fixing upon an individual which was just coming to rest. 

 This bacterium was then kept continuously in view, and, after assuming 

 a position perpendicular to the wall, it could be distinctly seen slowly 

 forcing its way through until finally it emerged into the cell-cavity. 

 The penetration of the wall was subsequently observed on several 

 occasions, and numerous individuals could be seen in all stages of the 

 process. The time required varied with the thickness of the wall, but 

 on an average occupied about 3 hours. To give a special instance, a 

 particular bacterium which was found to be just entering the wall at 

 11.30 A.M. emerged at 2.10 P.M. (fig. 1). 



jFig. 1. — Pseudomonas destructans passing through a cell-wall. The bacterium 

 was observed to enter the cell-wall at 11.30 A.M. (A) and to emerge into the 

 cell at 2.10 P.M. (B). (Hanging drop ; Zeitz ofcj. 7, oc. 4.) 



The observation of the movements of the bacteria, though difficult 

 and very trying, was yet considerably furthered by the different re- 



