370 The Microscope. 



6. Apply an even coat of good amber or copal varnish. I 

 find good copal varnish, called " Elastic Gear Varnish," and 

 used on carriage gearing, better than any gold size. It has to 

 go through mud, rain, sand, the burning sun, expansion of heat 

 and contraction of cold, on carriages and railroad passenger 

 ears. The body of the ring should be hard, solid, tough, 

 elastic, and above all, devoid of brittleness ; it should be built 

 up to the top of the cover glass and finished with the best 

 amber or copal varnish. 



To make a colorless copal varnish select the palest lumps of 

 copal gum and crush them into small pieces, but do not pul- 

 verize when full of dirt; tie in a bag of fine muslin, and sus- 

 pend in a wide mouth bottle of sulphuric ether, when the copal 

 will gradually ooze out into the ether. When the gum has 

 been digested, let the bag drain off and be thrown into another 

 bottle of ether, which will remove all the available gum. It is a 

 good plan to have plenty of the gum so that the liquid will 

 form a varnish sufficiently thick. Then add oil of caraway or 

 any slow drying essential oil, as oil of anise or poppy or sweet 

 almonds, which are as colorless as possible in such small 

 quantities ; this will make the varnish dry more slowly and 

 render it more elastic. When it dries properly, 3^et is too 

 thick, add oil of rosemary or some such colorless essential oil 

 that it may dry about as fast as may be required. If it should 

 dry too slowly add more ether and mix thoroughly. 



Some of the essential oils, although colorless, have slightly 

 colored my varnish, yet it is the most colorless varnish I ever 

 saw. It is elastic, dries hard and endures the test admirably, 

 and is very tenacious ; it is easily prepared in the way described. 



A Russian ph^ysician has succeeded in cultivating vaccine 

 virus, and finds that the virus, artificially cultivated, is as effec- 

 tive as the genuine, and has the advantage of absolute purity, 

 so that its use involves no danger from scrofula, tuberculosis, 

 or other constitutional diseases. — The Pacific Rec. Md. and 

 Surg. 



Prof. Christopher Johnson, a well-known microscopist, died in 

 Baltimore, Oct. llth, aged sixty-nine years. 



