1899J MICROSCOPICAL JOURNAL. dd 



other was of a yellow tint g"ot from oxide of mang-anese 

 and iron, M. Henri Cross finds that objects which to the 

 naked eye appear the same in color, look different throug-h 

 the screen. Thus a green emerald looks a rosy violet 

 through the glass, but a false green emerald looks green. 

 True sapphire keeps its natural blue through the screen, 

 and false blue sapphire appears a rosy red. An Egyptian 

 cup of Sevres blue paste appeared blue, save a part re- 

 stored, which was red. He was able to conclude that the 

 Egyptian paste had a base of copper blue and the restored 

 part one of cobalt. — Optical Journal. 



MICROSCOPICAL MANIPULATION. 



Spirit-Proof Micro-Cement.^ — ^Take Nelson's amber gel- 

 atine, soften with water, pour off the water, melt the gel- 

 atine with gentle heat. Add suf&cient white lead in powder 

 to render it opaque. 



Focal Lengths. — It is not an easy matter to measure ac- 

 curately the focal lengths of microscopic objects ; but a 

 sufficiently close approximation can be obtained by com- 

 paring them with others, whose focal lengths are known, 

 taking care to use the same eyepiece and the same tube- 

 length. The best way of measuring the power of any 

 combination of objective and eyepiece is to place a stage- 

 micrometer on the stage and compare the graduations as 

 seen through the instrument with one eye with an ordinary 

 foot-rule, as seen at the same time with the other, both 

 eyes being open and the rule being at a distance of 10 in. — 

 A. WooLSEY Blacklock, M. D. 



New Stain. — Ziemann has described a new stain for de- 

 monstrating the nucleus of the malarial parasite. He uses 

 various proportions of a one-per-cent watery solution of 

 rectified methylene blue and a one-per-cent watery solu- 

 tion of eosin. He demonstrated throughout the body of 

 the parasite certain reddish stained areas. 



To Kill Invertebrates. — Take four parts of a saturated 

 aqueous solution of corrosive. sublimate and add to it one 



