10 MEDICAL BACTERIOLOGY 



If the oil immersion lens is to be employed, first place a drop of immersion 

 oil on the slide or cover glass and with the eye fixed on the objective focus down- 

 ward until the objective touches the oil and almost, but never quite touches 

 the cover glass. Then look in the ocular and slowly focus upward until the field 

 comes into view. Never touch the cover glass with the lens. 



FIG. i. MICROSCOPE SUITABLE FOR GENERAL PATHOLOGIC AND BACTERIOLOGIC WORK. 

 a. Ocular or eye-piece, b. Draw-tube, c. Rack. d. Milled head of pinion moving the 

 rack; the rack and pinion (c and d) together are called the coarse adjustment, e. Micro- 

 scopic tube. /. Micrometer screw by which the fine adjustment is operated, g. Triple 

 nose-piece or revolver which receives the objectives, h; in the above instrument there are 

 three objectives which in turn may be rotated into the optical axis. i. Stage on the upper 

 surface of which are clips for holding the slide during examination, j. Iris diaphragm in 

 substage condenser; the diaphragm permits variation in the quantity of light admitted, and 

 the condenser properly focuses the rays on the object examined, k. Screw for raising and 

 lowering the condenser by which the latter, when not in use, may be thrown to the side. /. 

 Mirror for reflecting light into the optical axis of the instrument, m. Inclination joint per- 

 mitting inclination of the instrument. The vertical column below the inclination joint is 

 called the pillar and is solidly joined to the large, heavy, horseshoe base supporting the 

 instrument. 



A focus is first obtained with the coarse adjustment; not until the best focus 

 possible to obtain with it has been reached, do we use the fine adjustment. 



The fine adjustment has a very limited range and should never be given more 

 than half a turn one way or the other. It is delicate, easily injured, and once 

 out of order requires the services of a skilled mechanic to adjust it. 



When any part of the microscope becomes loose or out of order, unless one 



