4 THE MICROSCOPE. 



blue, the cartilage bones yellow, and the membrane bones either 

 red or white ; when drawing the bloodvessels colour tlie arteries 

 red and the veins blue. 



V.-THE USE OP THE MICROSCOPE. 



The microscope consists essentially of a stand and a hody, the 

 latter of which bears at its ends the lenses by which the magni- 

 fying power is obtained. 



The stand is an upright pillar, the lower end of which is 

 attached to a heavy foot to ensure steadiness. A little way 

 above the foot the stand supports a horizontal plate — the stage — 

 on which the object to be examined is placed. The stage is 

 perforated in the middle by a hole, the size of which can be 

 varied by means of diaphragms. Through this hole light is 

 directed on the object to be examined by means of a mirror 

 attached to the stand below the stage. Above t-he stage the 

 stand supports a vertical tube, in which the body of the micro- 

 scope slides up and down. 



The body is a tube, in the upper end of which is placed a 

 combination of lenses, known as the eyepiece, while to the lower 

 end is screwed another combination of lenses — the objective. 



A microscope is usually provided with a couple of eyepieces 

 and a cou]3le of objectives of different magnifying power. An 

 objective magnifying only a small number of times is called a 

 loiv 'power ; one magnifying many times (200 diameters or more), 

 a liigh power. Similarly eyepieces are spoken of as high or low 

 according to their magnifying power. 



In order that an object may be seen clearl}^ the objective 

 must be at a certain definite distance from the object, this 

 distance varying with different objectives, and to a slight extent 

 with different observers. The higher the power employed the 

 closer must the objective be brought to the object. As the 

 position of the object on the stage of the microscope is fixed, 

 this distance is regulated by moving the body of the microscope 

 up and down in the tube in which it slides. 



This process of focussing is effected in two ways : — 

 (1) By simply sliding the body up and down by hand : this, 

 is known as the coarse adjustment ; it should be performed with 

 a slight screwing motion, and can only be used Avhen low 

 powers are being employed. 



