ZENTMA YERS MECHANICAL FINGER. 293 



The process of arranging diatoms is a simple one, easily 

 done by means of a small camel's-hair pencil, with the aid 

 of the erector and a half-inch objective. The brush should 

 be drawn through the lips, and when using the microscope- 

 stand shown in Fig. 24, sitting well over it, the side of the 

 hand only resting on a support, it is quite easy after a little 

 practice to remove any diatom from the field of view. 

 For this purpose many workers use what is called a 

 mechanical finger as a substitute for the fingers of the 

 human hand. Zentmayer's form has been described in the 

 ' Monthly Microscopical Journal/ and is here reproduced as 

 Fig. 239. 



FIG. 239. 



Rezner's form of this instrument (Fig. 240) is much more 

 simple than the above, and may be adapted to any micro- 

 scope. It consists, as may be seen in the engraving, of a 

 sleeve, which is passed up over the objective just far enough 

 to possess a firm bearing, and so that the point of the 

 bristle is in focus when depressed to nearly its full extent. 

 In order to use this finger, the point of the bristle should 

 be brought into the centre of the field, touching the object 

 slide, and then withdrawn, still in the axis of the micro- 

 scope, until it has become invisible. The desired object is 



