110 PHOTOGRAPHING BACTERIA. 
heavy block of wood B; this can be pushed back upon the baseboard which 
supports it, so as to-allow the operator to place his eye at the eyepiece of the 
microscope. When it is brought forward an aperture of the proper size ad- 
mits the outer extremity of the eyepiece and shuts off all light except that 
coming through the objective. Cis the microscope, and D the Abbe con- 
denser, supported upon the substage. Ejisa thick asbestos screen for pro- 
tecting the microscope from the heat given off by the battery of gas burners 
F. This asbestos screen hasan aperture of proper dimensions to admit the 
light to the condens-r D. The gas burners are arranged in a series, with 
the flat portion of the flame facing the aperture in the asbestos screen EH. 
The concave metallic mirror G is properly placed to reflect the light in the 
desired direction. I have not found any advantage in the use of a condens- 
ing lens other than the Abbe condenser upon the substage of the microscope. 
The focussing is accomplished by means of the rod I, which carries at one 
extremity a grooved wheel, H, which is connected with the fine adjustment 
screw of the microscope by means of a cord. . 
‘‘The focussing wheel J may be slipped along the rod I to any desired 
position, and is retained in place by aset screw. The rod I is supported 
Pron 
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Fie. 74, 
above the camera by arms depending from the ceiling, or by upright arms 
attached to the baseboard. 
‘“‘T have lost many plates from a derangement of the focal adjustment 
resulting from vibrations caused by the passing of loaded wagons in the 
street adjoining the laboratory in which I work. This has been overcome 
toa great degree by placing soft rubber cushions under the whole appa- 
ratus.” 
I have recently (1895) seen a gaslight which I believe would prove 
to be a valuable substitute for ordinary street gas, and I judge that, 
owing to its superior brilliancy, a single jet would suffice to replace the 
five burners in a linear series which are shown in the above figure. 
The gas referred to is acetylene, which may now be obtained in a 
liquid form in strong metal cylinders. Reference has already been 
made to the use of an oil light, and for low powers an ordinary lamp 
with a flat wick may be used. That bacteria may be successfully 
photographed, with an amplification of one thousand diameters, by 
means of an oil lamp is shown by the beautiful photomicrographs 
made by Capt. W. C. Borden, Assistant Surgeon U. 8S. Army. 
At my request Dr. Borden has prepared the following detailed 
account of his method: 
‘From Johns Hopkins University Circulars, vol. ix., No. 81, p. 72. 
