516 HISTOLOGY 



focus, and the continuous use of the fine adjustment distinguishes an 

 experienced microscopist from a beginner. Both eyes should be open 

 (as will be natural after becoming accustomed to the instrument). 

 Often one acquires the habit of using only the right or the left eve for micro- 

 scopic work, but it is better to learn to use both. 



Always examine a specimen first with a low power objective and then 

 with a high power. In focussing the microscope, have the objective 

 drawn away from the slide and focus down. This should be done cau- 

 tiously, with a portion of the specimen actually beneath the lens; if there 

 is only cover glass and damar there, the objective will probably be driven 

 down upon the slide. Unless one is sure that stained tissue is in the field, 

 the slide should be moved back and forth as the objective is being lowered. 



In working with the Abbe condenser, the flat surface of the mirror 

 should be uppermost, provided that it is used in daylight and the rays 

 falling upon it are therefore parallel; but for the divergent rays of an arti- 

 ficial light near at hand, the concave mirror may be used, and the light 

 may advantageously be made to pass through a blue glass, which lessens 

 the yellow glare. 



The objectives must never be scratched. Lens paper or fine linen 

 should be used to wipe them. If they are soiled with damar they should 

 be wiped with a cloth moistened with xylol, but since the lenses are 

 mounted in balsam, xylol must be applied to them cautiously. A mi- 

 croscope of the kind shown in the figure should never be lifted by any 

 part above the stage, lest the fine adjustment be damaged; the pillar 

 should be grasped below the stage. 



RECONSTRUCTIONS. 



There is an important arrangement of mirrors (Abbe's camera lucida) 

 for drawing the outlines of sections. It is attached to the microscope 

 above the eye-piece, and on looking into it one can see the image of the 

 section beneath the objective apparently spread upon the drawing paper 

 beside the microscope. Thus the pencil point can be seen as it is made to 

 trace the outline on the paper. With a little practice the same result 

 may be obtained more or less perfectly without the camera, by looking 

 into the microscope with one eye and at the same time upon the paper 

 with the other. This possibility was noted by the early microscopists, 

 and it is a useful accomplishment. More satisfactory than the camera 

 lucida is the projection apparatus of Edinger, arranged with an arc light, 

 whereby the image of the section is projected through an inverted micro- 

 scope upon the drawing paper beneath. With the camera, or projection 

 apparatus, a succession of serial sections may be drawn with the uniform 

 magnification essential for reconstructions. The magnification is deter- 



