JOUENAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
SEPTEMBEE, 1878. 
I. — On the Measurement of the Diameter of the Flagella of 
Bacterium termo : a Contribution to the Question of the 
Ultimate Limit of Vision ” with our jpresent Lenses, By 
Eev. W. H. Dallinger. 
{Bead before the Eoyal Microscopical Society, June 5, 1878.) 
Plates VIII. and IX. 
It will be remembered by this Society that two years ago, having 
in conjunction with Dr. J. J. Drysdale completed as far as we then 
purposed a series of observations on the life-histories of a group of 
monads, we determined to use the experience thus gained, and if 
possible to study in a similar way the Bacteria. We commenced on 
B. termo ; and our first object was to make out clearly its normal 
form, and to discover if possible the agency by which movement 
was effected. 
In the case of the large form known as Spirillum volutans, 
DESCRIPTION OF PLATES. 
Plate VIII. 
Fig. 1. — Bacterium termo x 4000 diam. 
„ 2. — Spirillum volutans x 2000 diam. 
„ 3. — Vibrio rugula x 2000 diam. 
„ 4. — Spirillum undula X 3000 diam. 
„ 5. — Bacillus ulna x 3000 diam. 
Plate IX. 
Fig. 6. — Bacterium lineola x 3000 diam. 
„ 7. — Photograph of Bacillus subtilis, showing flagella. By Dr. Koch x 500. 
„ 8. — Ditto, ditto (or as Dr. Koch thinks a variety, B, amylobacter), also 
photographed, and faintly showing flagella x 700 diam. 
Fig. 9. — Bacillus subtilis X 4000 diam. 
,, 10. — B. termo. 
„ 11.— A camera lucida outline of the lower part of B. termo, magnified 
2000 diam. c is the pencil line intended to cover the image of a part of the 
flagellum ; and a represents by dots the part of the image with which the line 
can be compared. 
Fig. 12 is the above drawing placed on the stage of the microscope, and 
magnified 5 diam. In this way the ratio between the diameter of the body of 
the Bacterium and the diameter of the flagellum can be compared by means of 
the wires of a screw micrometer. The ratio here .shown being as 10 to 1. 
VOL. I. O 
