CHAPTER XIX 

 MICROSCOPE ACCESSORIES 



MECHANICAL STAGE 



THE device known as the mechanical stage is 

 essential in work requiring the systematic exami- 

 nation of several fields or all parts of the specimen. 

 It is used in the quantitative estimation of the differ- 

 ent types of cells in blood samples; in the exami- 

 nation of urinary sediments, and in bacterial, mold 

 and spore counts. The more complicated types of 

 microscopes are provided with mechanical stages 

 which are permanently attached to the instrument. 

 This construction presents the advantages of rigidity 

 and fixed position. However, these fixed mechanical 

 stages are often inconvenient and are liable to cor- 

 rosion if temporary mounts are frequently used. To 

 overcome these faults many manufacturers supply 

 an extra, or plain, stage, which is interchangeable and 

 can be substituted for the fixed mechanical stage. 

 The attachable mechanical stage serves all purposes 

 and is the type generally used. It consists of a verti- 

 cal frame firmly attached to a horizontal frame, the 

 latter part of the apparatus being equipped with slide 

 clips. Movement of the frames in vertical and hori- 

 zontal directions is secured by milled wheels attached 

 to geared pinions, the teeth of which are fitted to racks 

 upon the frames. Each frame bears a graduated 

 scale which, in combination with a vernier, reads 



213 



