APPENDIX. — USE OF THE MICROSCOPE. 203 



APPENDIX TO PART II. 



Use of the Microscope in Vegetable Histology. 



Kind of Microscope Required. It is a mistake to suppose that a complex 

 and costly instrument is essential to obtaining a good knowledge of vegetable 

 histology. The optical parts must, of course, be of good quality, but it is 

 better that the stand should be simply constructed, for its use will then be more 

 easily learned and there will be fewer parts liable to get out of order. A stand 

 of small size, built after the so-called continental model, is far preferable to the 

 larger English and American ones, both because it is more convenient to handle, 

 and because, in much of the work required to be done it is better, on account 

 of the frequent necessity of applying reagents to the tissues undergoing investi- 

 gation, to have the stand in the upright position with the stage horizontal. To 

 work with the instrument upright, if the stand is a large one, is both incon- 

 venient and tiresome. 



Referring to Fig. 460, the parts of a compound microscope are as follows : 

 A is the eye piece, which, in its usual form, consists of two planoconvex lenses, 

 mounted in a metal tube, the one placed next the eye, called the eye-lens, and 

 the one farthest from the eye, the field- lens ; B is the objective, consisting of a 

 combination of lenses mounted in a metallic frame, and the rest of the instru- 

 ment is called the stand. Of the latter, the tube or combination of tubes which 

 hold the optical parts, is called the body ; this ordinarily consists of two parts, 

 the tube T, and the sleeve, C, in which the tube slides. The sliding of the tube 

 within the sleeve constitutes, in this case, the coarse adjustment or means by 

 which the microscope is approximately focused. Supporting the body is the 

 arm, D ; this is surmounted at the top by a. fine adjustment screw, E, by means 

 of which the body may be moved slowly up or down, so as to bring the object 

 accurately into focus. Rigidly attached to the basal part of the arm, and with 

 its plane at right angles to the axis of the body, is the stage, F, on which the 

 object to be studied is placed. The stage has a central aperture for admitting 

 light from below, and, on its upper surface, is provided with two spring clips to 

 secure the slide that holds the object. Attached to the under surface of the 

 stage is a revolving diaphragm, G, perforated with apertures of various sizes to 

 regulate the amount of light admitted to the objective. Below the stage is the 

 mirror, H, to reflect light upward through the aperture in the stage upon the 

 object. The part of the stand which supports the stage, arm and body, with 

 the optical parts, is called the pillar, J, and this, in turn, is supported by a 

 heavy piece of metal called the base. 



The requisites of a microscope suitable for a course in vegetable histology 

 may be summed up briefly as follows : 



