MICROSCOPICAL DIAGNOSIS. 13 



fully extended, the length of the tube will be fixed, and with the aid 

 of the stage micrometer the value of the spaces of the eye-piece 

 micrometer for the various objectives and eye-pieces, is reckoned 

 once for all. This is done in the following manner: Bring in focus 

 the lines of the stage micrometer, place the eye-piece micrometer in 



Fig. 5. Eye- Piece Micrometer. (Increased one-third.'] 



its proper position in the eye-piece, notice how many spaces on the 

 eye-piece micrometer cover a single space on the stage micrometer, 

 then divide the distance between two lines on the stage micrometer 

 by the number of spaces covered on the eye-piece micrometer 3 ; the 

 result will be the value of each spaqe on the eye-piece micrometer 

 for that particular ocujar and objective. 



Using the one-fourth inch objective and "C" eye-piece, we will 

 assume that five spaces on the eye-piece micrometer cover one 

 space on the stage micrometer r-iooo of an inch then one space 

 on the eye-piece micrometer would be equal to one-fifth the value 

 of the five spaces, viz., 1-5000 of an inch. 



Now remove the stage micrometer and place in the field a spec- 

 imen of blood for instance, and a white blood corpuscle is seen just 

 to cover two spaces on the eye-piece micrometer; it is the 2-5000 

 of an inch in diameter. 



A number of additional accessories will be added to the micros- 

 copists' outfit as their demand becomes manifest. 



There are several methods by which the magnifying 

 power of a microscope can be determined. The follow- 

 ing are convenient: Incline the instrument until the 

 centre of the eye-piece is ten inches from the table; 

 the lines of a stage micrometer are then accurately focused; by 

 means of a camera lucida or neutral tint reflector the magnified 

 image of the lines is thrown upon a sheet of paper resting on the 

 table just beneath the eye-piece. The eye is placed as seen in the 

 figure, and the lines are traced with a pencil and their distances 



