170 



BACTERIA IN RELATION TO PLANT DISEASES. 



X.650 



Fig. 139* 



dale's conception of this organism, at a time when the air was full of talk of Cohn's 

 researches, is shown in fig. 140. Dallinger & Drysdale's drawings were made from 



unstained material, and there is no doubt that 

 these expert microscopists actually saw what they 

 figured, viz, a schizomycetous organism provided 

 with one polar flagellum and belonging to the 

 family Bacteriacese. Dallinger afterwards care- 

 fully measured the diameter of the flagellum many 

 times over in unstained material, grown in Cohn's 

 fluid. 



As bearing on the question whether Ehrenberg 

 could see the flagellum of an unstained bacterium 

 with the microscopes at his disposal, it is inter- 

 esting to note Dallinger's statement that Koch could not see the unstained flagellum 

 of Bacterium termo because he used " low-angled glasses, which are incompetent to 

 that demonstration." Another remark of Dallinger is also 

 pertinent. "I have learned," he says, "from experience 

 that there is as great a diversity in different individuals in 

 the sensitiveness of the retina as there is in sensitiveness 

 of the olfactory or auditory nerves." 



The writer's own conception of Bacterium termo is shown 

 in fig. 141. These organisms are green-fluorescent species 

 cultivated in Cohn's solution, from water into which beans 

 had been thrown in the manner described by Cohn. The 

 very distinct flagella were stained by Lowit's method. The 

 particular species from which this was obtained did not 

 liquefy gelatin. 



To the writer, then, the genus Bacterium is Bacterium 

 (Cohn emend.), and is based on the morphology of the green-fluorescent organisms, 



capable of growing in Cohn's nutrient solution and 

 called by him Bacterium termo.\ It corresponds 

 to Migula's genus Pseudomonas, for which name it 

 should be substituted as a proper generic name for 

 stra ig nt or slightly curved Bacteriacese, motile by 

 means of one to several polar flagella. It includes 

 most of the yellow bacteria and all of the green-fluor- 

 escent bacteria (vide Migula's system, Bd. II, p. 875). 



x? 



X GOO ca 

 Fig. I40.t 



(S* 



100 



m m 



Fig. 1414 



*Fic. 139. Bacterium termo: a, motile form; b, zoogloese. After Cohn. Untersuchungen iiber 

 Bakterien. Beitrage z. Biol. d. Pflanzen, Bd. I, Heft 2, Plate III. 



tFic. 140. Dallinger and Drysdale's conception of Bacterium termo. See Dallinger and Drys- 

 dale " On the Existence of Flagella in B. termo." Monthly Micros. Jour., Sept. i, 1875, Plate 

 CXIII, p. 105, figs. 6 and 7. 



JFiG. 141. The writer's conception of Cohn's Bacterium termo. Organism obtained by throw- 

 ing beans into water and then making a transfer from the green-fluorescent liquid to Cohn's solu- 

 tion. Stained by Lowit's method. X 2000. 



gThese organisms have no necessary connection with Bacterium termo Ehrenberg or with 

 Monas termo Muller. We shall never know what these were. 



