MrCROSrOPICAL TECHNTQUE. 319 



half a gramme of carmine, 20 cc. of absolute alcohol, 30 drops of 

 hydro-chloric acid, and then adding 25 grammes of chloral hydrate. 

 The solution when cool is filtered. 



A Pneumatic Bubble Remover."*^— Mr. A. P. Weaver having 

 been annoyed with air-bubbles in his mounts, has devised a simple 

 air-pump for removing them as follows : — Take a small rubber 

 syringe, the packing on the cylinder of which ought to be adjust- 

 able so as to fit the body of the syringe rather tightly, cut off the 

 nozzle rather close to the body, and bore a hole 3 mm. in diameter, 

 near the top of the latter, so that the packing will always be below the 

 hole. Cut from an old rubber boot two washers 2*5 cm. in diameter, 

 and with a central aperture of 2 cm. ; cement these washers together 

 with Red Cross cement (such as is used for mending punctures in 

 pneumatic bicycle tyres) ; cut from the boot two more washers of 

 the same outside diameter, and with a central hole a little smaller 

 than the nozzle of the syringe ; cement these last two washers 

 together also, and cement them to the first two prepared ; you will 

 now have a shallow chamber a little larger than the cover-glass ; 

 force the nozzle of the syringe through the opening in the two top 

 plates and firmly cement it there. All these joints must be air-tight. 

 To use the instrument, place the slide on a smooth surface, wet 

 the under surface of the rubber washers and apply the same to the 

 slide, with the cover-glass in the shallow chamber. To make a 

 good air-tight contact with the slide, grasp the syringe with 

 the left hand and allow the lower side of the latter to 

 hold the washers firmly to the slide. The hole drilled in 

 the syringe is to act as a trap or valve, and is to be tightly 

 covered with the first finger of the left hand (keeping the latter in 

 position, grasping the syringe and holding the washer to the slide), 

 at each downward stroke of the piston and uncovered at each 

 upward stroke. This is, of course, done to prevent the entrance 

 of air to the vacuum chamber beneath, after it has once been 

 exhausted. I have found that three or four strokes are sufficient 

 to bring all bubbles to the surface of the mounting fluid and cause 

 them to burst. 



* The Microscope. N.S., Vol. I. (1893), p. 41. 



