THE MICROSCOPE AND ITS ACCESSORIES. 5 



gmis. of pure common salt in 1000 cc. of water. As this fluid is 

 apt to undergo change, it should not be kept too long. 



(2.) Glycerine (either pure or equal parts of glycerine and water). 



(3.) Balsam, either Canada balsam or dammar (p. 85). 



(4.) Farrant's Solution (p. 85). 



(5.) Dilute Acetic Acid (2 per cent.). 



(6.) Hsematoxylin Solution (p. 68). 



(7.) Picro-Carmine (p. 66). 



(8.) Clove-Oil or Xylol. This should be provided with a small 

 brush fixed on the end of a wooden rod perforating the cork. 



17. Other Apparatus is required, but in a well-equipped 

 laboratory special articles are supplied as required ; they are referred 

 to in the context. They include a dissecting microscope, photophore, 

 mounting block, warm stage, eye-piece micrometer, lamp, turntable, 

 polarising apparatus, camera lucida, &c., &c. 



II. THE MICROSCOPE AND ITS ACCESSORIES. 



1. An account of the optical principles on which the microscope 

 is constructed is purposely omitted. The compound microscope 

 consists of a stand fixed to a heavy, usually horse-shoe shaped, foot. 

 The stand (fig. 9) carries a stage to support the microscopic 

 preparation, the mirror or arrangement for illuminating the object, 

 together with the body tube ; the latter consists of a long brass tube, 

 or one tube telescoped into another. To the lower end of this tube 

 is fixed a combination of lenses, constituting the lens or objective, 

 while at its upper end is the eye-piece. 



2. The tube is blackened inside, and to its lower end is screwed 

 the objective, consisting usually of several lenses screwed together. 

 By means of it a magnified inverted aerial image is produced in the 

 body of the tube. The lenses on the objective should not be 

 unscrewed. At least two objectives are required a low power 

 and a high power. 



At the upper end of the tube is the ocular or eye-piece, com- 

 posed of two plano-convex lenses, the one next the eye of the 

 observer being called the eye-glass, the lower one the field-glass. 

 The two lenses, with their convex surfaces downwards, are fixed in 

 a brass tube which slips into the upper end of the tube of the 

 microscope. 



3. The tube itself is supported in a vertical position on the stand, 

 so that it can be moved upwards and downwards vertically, to bring 

 the objective near to the object, and thus bring the latter clearly 

 into focus. This arrangement is termed the adjustment. The 



