MICROSCOPES. 417 



Microscopes of a certain grade are required, and if they cannot be 

 afforded, no instrument should be bought. The necessary equipment, as 

 shown in the figure, is a stand with fine and coarse adjustment ("microm- 

 eter screw" and "rack and pinion") and a large square stage. The more 

 expensive round and mechanical stages are not necessary. There should 

 be an Abbe condenser (with iris diaphragm), a triple revolver, a high and 

 a low 7 eye-piece or ocular, and the following objectives: a inch and a 

 or | inch, which must be parfocal, together with a T V oil immersion for 

 cytological and bacteriological work, and a 2 inch (very low power) for 

 embryological work. The T V oil immersion is an expensive objective, 

 and its purchase may be postponed. The 2 inch is a cheap objective which 

 is very useful in obtaining a view of an entire section, and for embryological 

 reconstructions it is essential. The price of such an outfit, including the 

 oil immersion objective, is from $70.00 to $90.00. 



Satisfactory microscopes of American manufacture are made by the 

 Bausch & Lomb Company. A sample submitted by the Spencer Lens 

 Company to the Harvard Embryological Laboratory is also quite satis- 

 factory. The Leitz microscopes, made in Germany, are preferred by some 

 to the American instruments just described; they are not much more ex- 

 pensive. All agree that the Zeiss microscopes (German) are the best (and 

 most expensive) . It is undoubtedly true that any of these instruments will 

 fill the requirements of medical students and physicians. If the micro- 

 scope is purchased by a student unfamiliar with its use, it is well to have the 

 lenses examined by a disinterested microscopist. 



For a description of the nature and use of the microscope, the student 

 is referred to the gth edition of "The Microscope," by Professor S. H. Gage, 

 (Comstock Pub. Co., Ithaca, N. Y.). 



For the sake of emphasis it may be said that the microscopist works 

 with his right hand upon the fine adjustment and his left hand upon the 

 slide. As the latter is moved about, bringing different fields into view, 

 the focussing is done with the adjustment and not with the eyes. 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 eye for microscopic work, but it is better to learn to use both. 



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

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

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

 ly, 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. 

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