24 The Microscope 



Setting up the high-power ( X 40 ) lens should never be attempted until 

 the student is well practiced in steps 1 to 3. Then: 



4. (Fig. 23.) After the object which it is desired to study under the 

 high power has been located under the medium power, rack up the 

 body and turn the high power into place. Then, looking in from the side 

 as in the illustration, lower the high power with the coarse adjustment 

 until it not quite touches the coverslip. 



5. (Fig. 24.) While looking through the microscope, bring the lens 

 up with the fine adjustment until the object comes into focus. 



All this is so simple that only two things can go wrong and these are 

 easy to correct. 



1. The fine adjustment jams before the object comes into focus. Correct 

 by racking the tube up until the lens is well clear of the slide. Spin the 

 fine adjustment down (i.e., away from you) until it reaches the end of its 

 travel. Then repeat steps 4 and 5. 



2. There is insufficient light with the high power even though the 

 image is sharp. This is caused by either of two things: 



a. The flat, instead of the concave, side of the mirror has been used. 



b. The light source, such as the gooseneck lamp in the illustration, 

 is too close to (not too far from) the mirror. The mirror acts as a 

 lens (refer back to Fig. 9). The nearer the light source is to the 

 mirror, the larger will be the image and the more diffuse the light. 

 The further away, within reason, the light source, the smaller will 

 be the image and the more concentrated the light. 



THE MEDICAL MICROSCOPE 



Specifications. The medical microscope, of which a typical example, 

 with its lamp, is shown in Fig. 25, is usually provided with the following 

 equipment. 



Stand. A horseshoe foot on which is mounted an inclinable body com- 

 posed of four parts: the mirror holder, the substage, the stage, and the 

 tube carrier. The mirror mount is the same as that on a freshman micro- 

 scope. The substage is a ring into which the condenser fits. This ring is 

 provided with rack-and-pinion focusing. The stage is usually furnished 

 with a detachable mechanical stage, a device for providing rack-and- 

 pinion controlled movement of the slide along rectangular coordinates. 

 The tube carrier has the same coarse and fine adjustments as the fresh- 

 man microscope. 



Tube. Most of these microscopes can be obtained either with a mo- 

 nocular tube, of the type shown, or with a binocular tube of the type 



