228 THE AMERICAN MONTHLY [July 



But a simple and efficient oblique lig-ht illumination is desi- 

 rable. It is made in the following- manner : A piece of 

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

 tions, % inch long- and about /i 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 usin^ a 

 whetstone with a fine g-rain. The rod is g-round down 

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

 a lens with parallel sides. It is cemented, the g-round 

 side uppermost by means of a solution of Gum Thus in 

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

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

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

 object g-lass to be viewed is placed above it and wet 

 between them by means of Oil of Cassia. This allows 

 the lig-ht to pass throug-h and at the same time alters the 

 refractive ang-le so that an oblique ray can enter. At 

 the same time the lig-ht 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 ang^le of 150 deg-rees to axis of the micro- 

 scope. I find this illumination is very practical and bring-s 

 out the marking-s on fine -lined objects or "beaded dia- 

 toms" nicely. It is easy 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. Sunlig-ht is 

 best. Use Abbe condenser without a diaphrag-m, or with 

 the largest opening- of an iris diaphragfm. A 1-12 oil 

 immersion is necessary to clearly disting-uish. 



No objective yet made will bear this treatment and g-ive 

 critical imag-e. 



Gummy Media. — I once made some very satisfactory 

 mounts of Alg-ae, etc., in peach tree g-um dissolved, or. 



