xxiv INTRODUCTION. 



If specks are present, it may be easily determined as to whether they are on the ocular (eye- 

 piece) or on the objective ; if they are on the eyepiece, they will necessarily move when it is 

 moved. They must be removed by gentle cleaning with chamois leather. 



(a) Low POWER (L). With the No. 3 objective. Place the tube of the microscope so that 

 the lens is at least an inch and a half above the object. Keep looking through the micro- 

 scope, and, whilst doing so, keep the slide on the stage in motion with the left hand, and 

 rotate or twist the tube downwards always from right to left until the outline of the object 

 comes distinctly into view. Then employ the fine adjustment, and accurately focus the object. 



(b) HIGH POWER (H). With the No. 7 objective. Place the lens a quarter of an inch above 

 the object, and then slowly rotate the tube downwards, keeping the object on the stage in 

 motion all the time with the thumb and fore-finger of the left hand, until the object just comes 

 into view, then employ the fine adjustment. As already indicated the magnifying power may 

 be increased by pulling out the draw-tube. 



Movement of the Slide on the Stage. This is done most conveniently by means of the 

 thumb and fore-finger of the left hand. Never employ two hands to move a slide ; it is quite 

 unnecessary. By practice wonderful precision of movement is acquired. Two small clips are 

 placed on the stage, which serve to fix the slide, so that it remains in any position. All the 

 cumbrous mechanical appliances formerly in fashion for moving the slide on the stage are quite 

 unnecessary. 



GENERAL RULES FOR THE EXAMINATION OF AN OBJECT. 



Always begin the examination of an object with a low power, in order to obtain a general 

 survey of the arrangement of the parts. If it be desired to study any particular part, place it 

 directly in the centre of the field of the microscope by means of the low power, and then ex- 

 amine it with a higher power, taking care in the latter instance to use a small aperture of the 

 diaphragm. 



PREPARATION OF A SIMPLE OBJECT. 



A drop of blood or milk serves the purpose very well. Clean a slide carefully. Dip the 

 slide in water, and rub both surfaces at once with a towel which has been washed several 

 times, so as to get rid of all adherent threads. It is often convenient for the beginner to use 

 a coloured towel say, a red one for if he finds a coloured thread in the field of the micro- 

 scope, he knows that it has come from the towel. Place a small drop of the fluid to be ex- 

 amined on the centre of a slide by means of a clean glass rod. Apply a clean cover-glass, 

 taking care to prevent the entrance of air-bubbles. 



MEHODS OF APPLYING A COVER-GLASS. 



Seize by the edge a previously cleaned cover-glass with forceps, and allow the drop 

 of fluid to come in contact with the edge of the cover farthest removed from the forceps ; 

 gradually and slowly allow the cover-glass to descend obliquely until the fluid forms a uniform 

 stratum under the cover. There ought to be just a sufficient amount of fluid to fill out the 

 space between the slide and cover-glass. When forceps are not at hand, the cover may be 

 applied with the fingers. Take a cover by the margins, rest one edge on the slide close to the 

 drop, allow the fluid to touch the under surface of the edge of the cover, and slowly permit 

 the cover to descend obliquely. 



