l>28 THE AMERICAN MONTHLY [July 



But ii siui])lo ;ind efiicient oblique lij^^ht illumination is desi- 

 rable. It is made in the follo\vin<;' manner : A piece of 

 glass rod such as is used by chemists for stirring- solu- 

 tions, )4 inch long and about 'y inch thick is taken and the 

 round side ground down on a whetstone so that the ground 

 part is rather tine. This can be accomplished by using a 

 whetstone with a fine grain. The rod is ground down 

 about one-third — about two-thirds are left. We have -then 

 a lens w'ith parallel sides. It is cemented, the gfround 

 side uppermost by means of a solution of Gum Thus in 

 alcohol and colored blue to a glass slide. The blue is im- 

 parted to it b}' means of a blue dye such as is sold by 

 chemists and is an aniline dye. It is used downwards, the 

 object glass to be view-ed is placed above it and wet 

 between them by means of Oil of Cassia. This allows 

 the light to pass through and at the same time alters the 

 refractive angle so that an oblique ray can enter. At 

 the same time the light is colored blue, a color that is 

 pleasant to the eye and at the same time objects seen in it 

 can be seen with distinctness owing to the peculiar color. 

 The light is a kerosine lamp and the mirror is a concave 

 one placed at an angle of 150 degrees to axis of the micro- 

 scope. I find this illumination is ver}- practical and brings 

 out the markings on fine -lined objects or "beaded dia- 

 toms'' nicely. It is eas}- to make. If tried by some 

 reader will he let the results be reported? - A. M. 

 Edwards, M. D. 



MICROSCOPICAL MANIPULATION. 



Bacillus of Diphtheria. — In examination of stained bac- 

 teria, use all the illumination you can obtain. Sunlight is 

 best. Use Abbe condenser without a diaphragm, or with 

 the larg-est opening- of an iris diai^hragm. A 1-12 oil 

 immersion is necessar}- to clearly distinguish. 



No objective yet made will bear this treatment and give 

 critical image. 



Gummy Media. — 1 once made some ver\' satisfactory 

 mounts of Algae, etc., in peach tree gum dissolved, or, 



