A BINOCULAR jMICROSCOPE ARRANGED FOR THE 

 STUDY OF COLONIES OF BACTERIA 



GUILFORD B. REED 

 Queen's University, Kingston, Ontario 

 Received for publication July 24, 1921 



The binocular microscope arranged as described below has 

 been used in this laboratory for several years with so much 

 satisfaction and profit in the isolation of bacteria that a descrip- 

 tion of such a simple piece of apparatus may not be out of place. 



Every one who has examined colonies of bacteria or other or- 

 ganisms on culture media by the use of direct illumination from 

 below has experienced more or less difficulty. The medium is 

 frequently too opaque to admit sufficient light, especially in the 

 case of media contaming blood; some very small colonies have 

 the same refractive index, or so nearly the same refractive index, 

 as their medium that observation may be very difficult even 

 on transparent media. These difliculties ai-e obviated and ob- 

 servation greatly facilitated by viewing the colonies in light 

 reflected from the surface of the culture as is usually done in 

 using a hand lens for this purpose. To make such observa- 

 tions with higher magnification and greater ease w^e arranged a 

 binocular microscope with magnifications of ten and twentj^ 

 diameters in the following manner. The tube and focusing 

 apparatus was removed from the stage and base and attached 

 to an independent support so that its optical axis was at an 

 angle of 45° with the stage, though so arranged that the angle, 

 might be altered as desired (A, fig. 1). A small arc with a 

 condensing lens was supported so as to project a beam of light 

 at an angle of 45° with the stage and at right angles to the opti- 

 cal axis of the microscope. As this gave rather more Ught than 

 was necessary a 75-watt "daylight" lamp was supported about 



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