v of th<* Tni')ti/> (Brassicu napus). 453' 



organism produces oxalic acid, which acts as a toxin to the protoplasm 

 and, decomposing the calcium pectate, furthers the dissolution of the 

 cells ; and also there is the secretion of a cy tase, which has a destructive 

 action upon the cell-wall and intercellular substance. The question of 

 the parasitism of the bacteria thus stands in these respects on the same 

 platform as that of the fungi, and a complete homology is established 

 between them. 



At first I experienced considerable difficulty in staining the flagella. 

 Loeffler's method was first tried, but with no positive results ; it 

 enabled one, however, to notice two deeply stained portions at either 

 end of the rod. Van Ermengen's method also failed in spite of the 

 strictest attention to technique, but by gradually increasing the 

 strength of the silver nitrate, and finally iising a 2 per cent, solution, 

 the desired result was obtained, and the bacillus was then found to 

 possess one polar flayelluiu (fig. 6). It should be mentioned that the 

 practice of passing the cover-slip thorough a flame was discarded in 

 favour of drying the cover-slip at 60 C. in a water bath, the latter 

 method being more certain and giving better results. 



Fig. 6. Pseudomonas destritctans with single polar flagellum. (Swift's 1 /12th 

 apochvoinatic and compensating ocular 12.) 



Pmidomonas is aerobic. "A stab culture rapidly develops along the 

 track of the wire, forming a funnel ; the edge of the funnel reaches the 

 sides of the test-tube in about forty-eight hours, and gradually sinks 

 as the gelatine becomes liquid. The gelatine, however, is never wholly 

 liquefied, the liquefaction extending down the sides of the tube only 

 to a depth of about one and a half centimetres. If a layer of gelatine 

 is immediately poured above the stab and the test-tube placed in the 

 incubator, the track of the wire is clearly marked put as before, but 

 the colonies soon cease to develop, and all growth ceases after three 

 days. The tube may be kept for many weeks in this condition. 



Again, so far as my experiments show, the action of PseudonunuM 

 upon turnips and potatoes only takes place in the presence of oxygen. 

 The following are typical examples of experiments frequently repeated 

 and always with the same results : A flask holding about 250 c.c., 

 with a tightly fitting indiarubber cork perforated to admit two glass 

 tubes bent at right angles, was sterilised in the following manner. 

 The tubes were plugged at each end with cotton wool, and the plugs 

 pushed well into the tubes, the flask being also plugged with cotton 

 wool, and, together with the glass tubes, sterilised by dry heat. Mean- 



