II. THE EXAMINATION OF MICROSCOPICAL 



SPECIMENS. 



THE MICROSCOPE. 



It is unfortunate that the price of a microscope is prohibitive to 

 many medical students, and that some who might purchase instruments 

 at the beginning of their work wait until later. The .cost is now so 

 reduced that an increasing proportion of students can enjoy the advantage 

 of having a microscope of their own. 



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

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

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

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

 more expensive round and mechanical stages are not necessary, and 

 since mechanical stages are detachable, they may be obtained later if 

 desired. There should be an Abbe condenser (with iris diaphragm), a 

 triple revolver, a high and a low eyepiece or ocular, and the following 

 objectives: U i6-mm. (f-inch) and a 4-mm. (|- or |-inch) which must 

 be parfocal; together with a 2-mm. (iV-inch) oil immersion, for cytological 

 and bacteriological work; and a 48-mm. (2-inch), which is a very low 

 power, for embryological work. The figures indicate the distance of the 

 section from the objective when the specimen is in focus; the higher the 

 power, the nearer the objective is brought to the object. The 2-mm, 

 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. 

 It may be noted that microscopes are now being finished more extensively 

 in black enamel than in lacquered brass; the former is not damaged by 

 alcohol and is more desirable. Improvements have also been made in 

 the post and fine adjustment, so that the form shown in the figure, although 

 good, is not the best. 



Satisfactory microscopes of American manufacture are now made 

 but all agree that the Zeiss microscopes (German) are the best (and most 

 expensive). If the microscope 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 nth edition of "The Microscope," by Professor S. H. 

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



