INTRODUCTION. 



xxi 



ON THE USE OF THE MICROSCOPE. 



GENERAL DIRECTIONS. 



The microscope used in the Physiological Laboratory of the University of Aberdeen is 

 Hartnack's, model No. III. A. (fig. 4) with an eyepiece, or ocular, No. 3, and two objectives, or 

 lenses, Nos. 3 and 7. The combination of ocular No. 3 with objective No. 3, gives a mag- 

 nifying power of about 65 diameters linear, and ocular No. 3 and objective No. / about 300 

 diameters, with the tube drawn out. These powers are quite sufficient for beginners, and, 

 indeed, for most of the ordinary work. This microscope costs about jl. Higher magnifying 

 powers are supplied when they are required. 



Fig. 4. HARTNACK'S MICROSCOIT. No. III. A. 

 One- fifth Natural Size. The Condenser is attached 

 to the Body of the Microscope. 



Fig. 5. SWIFT'S COLLEGE MICROSCOPE. 

 With a Condenser attached to the Stage for examining 

 opaque objects. 



The magnifying power can be diminished or increased by pushing or pull in gout the draw- 

 tube. In fig. 4, the draw-tube is represented as drawn out. 



In Hartnack's microscope, the stand has a horse- shoe form, but many prefer the tripod form 

 (fig- 5) as made by Messrs. Swift and Son, University Street, London. In this microscope the 

 tube is cloth-lined, so that it moves easily, and the stage is covered with a glass plate which 

 enables the slide to move easily on it, and prevents it from being acted on by acids. 



The object-glass, objective, or lens, is the most important part of a microscope, and it is 

 necessary to see that a good lens be procured. The lens should be tested by a competent 

 microscopist before it is purchased. Coloured blood-corpuscles and salivary corpuscles are 



