170 BACTERIA IN RELATION TO PLANT DISEASES. 



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 Bacteriaceae. 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. * 600 ca 



To the writer, then, the genus Bacterium is Bacterium lg ' '* 



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

 i i capable of growing in Cohn's nutrient solution and 



called by him Bacterium tcrnioS. It corresponds 



) j to Migula's genus Pseudonumas, for which name it 



( should be substituted as a proper generic name for 



^-~, V "P * i ^^ , straight or slightly curved Bacteriacese, motile by 



^-^^ 



of one to several polar flagella. It 

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



pi | 4] j esceut bacteria (vide Migula's system, Bd. II, p. 875). 



*Fic. 139. Bacterium tcnno: a. motile form; h, xoogkeae. After Cohn. Untersuchungen tiber 

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



tFir,. 140. Dallinger and Drysdale's conception of Bacterium tcnno. See Dallinger and Drys- 

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

 CXI 1 1, p. 105, figs. 6 and ;. 



tFir.. 141. The writer's conception of Cohn's Kactcrium Icnun. Organism obtained by throw- 

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

 tn'ii Stained by Lowit's method. X 2000. 



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

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



