110 SELECTION AJfl) tfsfc 



of view, while Fig. 23 shows the hap-hazard way in which ex- 

 aminations are usually made, abundant room being left (as 

 shown by the small crosses) for the escape of important fea- 

 tures, Now, with ordinary clips, it is difficult to effect this, 



Fig. 22. Fig. 23. 



although it may be done by the aid of a plate of metal or vul- 

 canite, a little thicker than the glass object-slide, and having a 

 straight edge. The forward movement is made by pushing the 

 vulcanite plate, while by sliding the object along the edge of 

 this plate, we are enabled to examine a narrow strip, the width 

 of the field of view, as shown in Fig. 22. A somewhat similar 

 device is shown on the stage of Zentmayer's Histological Micro- 

 scope, Plate VI. When slightly modified, this device also 

 serves as a guide for the Maltwood finder. 



In the simpler forms of the stage, the object is held in place 

 by spring clips, which press it down, and under which it is 

 moved. These clips are frequently screwed to the stage, which 

 is a great mistake, as we are thus prevented from slipping them 

 off, so as to leave the stage entirely clear. They should always 

 be held in such a way that they may be instantly removed, and 

 they should also be very thin and springy, otherwise it is im- 

 possible to move the object with sufficient delicacy. 



The so-called glass stage, or Zentmayer stage, has come into 

 extensive use, and is very much liked by some. As made by 

 Zentmayer, it consists of a plate of glass, held against a brass 

 support by means of a spring, which /is pointed with ivory. 

 The friction of the glass plate upon its metal support is thus 

 easily adjusted, and may be either so reduced that the plate will 

 respond to the slightest touch, or it may be so firmly clamped 

 as to be practically immovable. 



