1894.] MICROSCOPICAL JOURNAL. 349 



be touched on account of its extreme fragility; if any 

 small crystals adhere to its surface, they must be washed 

 off by pouring over it a few drops of watery solution of 

 iodine. When dry the specimen should be placed for a 

 few minutes under a bell-glass, by the side of a watch- 

 glass, containing a few drops of tincture of iodine ; and 

 lastly, a little very-fluid Canada balsam should be drop- 

 ped on it, and a thin glass cover be applied without heat. 

 Specimens may thus be obtained of extreme thinness, 

 and half an inch in diameter, or even larger, possessing 

 scarcely the slightest color, and yet completely polariz- 

 ing transmitted light. 



The Maltwood Finder and Similar Devices. 



By A. C. STOKES, M.D., 

 From his new book "Microscopical Prasis." 



Reference has already been made to the difficulty of 

 finding a small object, or some special part of a larger 

 object, with a high-power unless a mechanical stage be 

 used. The field of the high-power objective is so small 

 that the chances of bringing the desired object within 

 its circumference are slight. Usually it is necessary to 

 substitute a low-power lens, bring the specimen within 

 its field, then to re-attach the higher-power objective, in 

 or near whose field the object should be. 



On mechanical stages there are commonly engraved 

 two sets of lines about one one-hundredth inch apart, 

 the scales resembling those of a micrometer. These are 

 intended to facilitate the finding of the object the sec- 

 ond time, the objective being noted, and the position of 

 the stage recorded as read from the horizontal and the 

 vertical scales on its surface. When the stage is again 

 placed in those positions, the same objective used, and 

 the slide laid on the object-carrier as it was before, the 

 object should then be in the field. 



