108 



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. C is the microscope, and D the Abbe con- 

 denser, supported upon the substage. E is a thick asbestos screen for pro- 

 tecting the microscope from the heat given off by the battery of gas burners 

 F. This asbestos screen has an aperture of proper dimensions to admit the 

 light to the condenser D. The gas burners are arranged in a series, with 

 the flat portion of the flame facing the aperture in trie asbestos screen E. 

 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 a set screw. The rod I is supported 



Fio. 74. 



above the camera oy arms depending from the ceiling, or by upright arms 

 attached to the baseboard. 



44 1 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 

 to a great degree by placing soft rubber cushions under the whole appa- 

 ratus." 1 



I have recently (1805) 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. S. 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. 



