THE AMERICAN H1STOLOGICAL STAND. 45 



liable to occur daily. It is then, in such cases, a posi- 

 tive convenience to be able to pull the body-tube out of 

 the jacket, cleanse the objective, and return to its place. 

 All this can be done in much less time than would be 

 required, Avere the instrument furnished with rack and 

 pinion, to unscrew the lens, cleanse, and screw in place 

 again. 



The greatest objection that the writer has to urge 

 against the Histological stand is this: When it is 

 placed in a vertical position, there is a liability of its 

 tipping forward. This can be prevented by clamping 

 the instrument to the table with a small iron clamp, 

 such as are used by carriage-builders and are sold at 

 the hardware shops for a dime. In this simple way the 

 stand is rendered as solid, more stable indeed than those 

 of the heaviest build. 



One of my correspondents, to whom I had stated the 

 above-mentioned objection, informs me that Mr. Zent- 

 mayer has made some changes in the foot, securing 

 thereby greater steadiness. 



Previous to the introduction of the Histological, it 

 was generally taken and accepted that the purchaser of 

 a cheap stand ought not, in the nature of things, to 

 expect an instrument capable of all work. To a slight 

 extent, and to a slight extent only, does the remark hold 

 good to-day, for the Histological has not the revolving 

 platform, for the measurement of angular apertures 

 (apertures can, however, be measured on the stand), 

 nor has it the circular graduated stage ; nevertheless, 

 the Histological will accomplish a larger variety of 



