ADJUSTING THE MICROSCOPE 273 



and adjust yourself to it l)y adjusting the height of the table 

 or chair. If the microscope is to be inclined pull back on the 

 fine adjustment pillar and not on the body tube. 



In nearly all histological work the object is seen by trans- 

 mitted light; that is, by light that shines through the object, 

 and this is accomplished by reflecting the light from below by 

 means of the mirror, and where high powers are employed 

 the light should pass through a condenser. The mirror has 

 a plane and a concave surface, and where there is a condenser 

 the plane surface only should be used, and without a condenser 

 the concave mirror can in a measure fill its place, but it does 

 not give so good results with high powers as does the conden- 

 ser. The condenser should have an iris diaphragm by means 

 of which the light can be adjusted to the object used, as will 

 appear later on. 



For histological work there should be a medium and a high 

 power objective, such as a f and a ^ in. or a i6 and a 4 mm., 

 mounted on a revolving double nosepiece, as shown in Fig. 

 147. Assuming that the microscope is thus equipped revolve 

 the lower power, that is, the f in. or the i6 mm. objective into 

 position (in the figure the higher power is shown in i)osition) 

 and get ready some object for examination. To begin with 

 there is nothing better than starch from the potato. To pre- 

 pare this for examination a glass slip and coverglass obtain- 

 able from dealers in microscope supplies will be necessary. A 

 good supply of these should be at hand. Clean a glass slip 

 thoroughly so that it is crystal clear when you look through 

 it; lay it flat and put a small drop of water on it near the middle. 

 Cut open a potato and with the point of a pocket knife scrape 

 up a very small portion of the pulp not more than the size of 

 two pin heads. Better take too little than too much. Put this 

 in the drop of water on the sli]). Clean a coverglass thoroughly 

 and lay it over the drop. The coverglass must, be put on with 

 some care else air bubbles will become entangled in the prepara- 

 tion, and they are a nuisance, particularly to a beginner who may 

 mistake them for some part of the thing he is studying. To 



iS 



