Ch. Ill] 



MARKERS AND MECHANICAL STAGES 



loi 



complete exploration of a preparation and for blood counting. Most 

 of the mechanical stages have scales and verniers by which an object 

 once recorded may be readily found again. 



§172. Marker for preparations (fig. 59). —This instrument 

 consists of an objective-like attachment which may be screwed into 

 the nose-piece of the microscope. It bears on its lower end a small 



ss 



S9 60 



Fig. S9-60. Markers for Microscopical Specimens. 



Fig. 59- The simplest form of marker. It consists of the part 55 with 

 the milled edge (M). This part bears the society or objective screw for at- 

 taching the marker to the microscope. R Rotating part of the marker. 

 This bears the eccentric brush (5) at its lower end. The brush is on the wire 

 (W). This wire is eccentric, and may be made more or less so by bending the 

 wire. The central dotted line coincides with 'the axis of the microscope. 

 The revolving part is connected with the "Society Screw" by the small 

 screw (5). 



Fig. 60. SS, R, and B. All parts same as with fig. 59, except that the 

 brush is carried by a sliding cylinder, the end view being indicated in B. 



brush and the brush can be made more or less eccentric and can be 

 rotated, thus making a larger or smaller circle. In using the marker 

 the brush is dipped in colored shellac or other cement and when 

 the part of the preparation to be marked is found and put exactly 

 in the middle of the field the objective is turned aside and the marker 

 turned into position. The brush is brought carefully in contact with 

 the cover-glass and rotated. This will make a delicate ring of the 

 colored cement aro"und the object (fig. 61). Within this very small 



