The Microscope. 221 



The trough consists of a metallic vessel provided with a thin 

 extension at one end near the bottom furnished with glass- 

 covered apertures above and below. The body of the fish be- 

 tween the gills and tail is wrapped with a strip of soft cloth, and 

 the trough being filled with water, the fish is placed therein,, 

 with its tail projecting into the extension between the glass 

 covers. The tank is arranged on the microscope stage with the 

 tail of the fish in position for examination. So long as the fish 

 remains quiescent, all goes well, and the beautiful phenomenon 

 may be witnessed with great satisfaction, but the subject soon 

 becomes impatient, and at the most inopportune moment either 

 withdraws its tail from the field or jumps out of the tank, thus 

 causing a delay which is sometimes embarrassing. 



The uneasiness of the fish is caused partly by its unnatural 

 position, and partly by the vitiation of the water. The latter 

 trouble has been remedied by the writer, by inserting a dis- 

 charge spout in one end of the trough, and providing a tube for 

 continually supplying fresh water. The other difficulty has 

 been surmounted by providing two wire grids, each having 

 spring clips at their ends for clamping the walls of the tank. 

 These grids are pushed downward near the body and head of 

 the fish, so as to confine the little prisoner closely without doing 

 it the least injury. With these two improvements the exami- 

 nation may be carried on comfortably for an hour or more. — 

 Geo. M. Hopkins in Sci. Am. 



A GOOD CEMENT. — An article in the May number of The Mic- 

 roscope prompts me to suggest a trial of a cement that I have 

 found useful. 



Gelatine dissolved in a 10 per cent, solution of potassium bi- 

 chromate. The solution should be kept in the dark and be just 

 thick enough to run easily from the brush. Wipe off" the sur- 

 plus glycerine, and spin on a ring of the bichromate gelatine and 

 expose to the sunlight. It soon hardens to an insoluble, horny 

 substance. A second ring of the same may be spun on in a day 

 or two, and afterward the mount may be finished with any other 

 cement or lacquer. 



I do not suppose that I am the first or only person who 

 thought of this, but I do not remember seeing it recommended 



