4 MANUAL OF HISTOLOGY. 



No good liistological work can be done without a note-book 

 to record the results of observation. All such memoranda will 

 be very useful for subsequent reference. A Jieating slide, a 

 gas chamber and a slide arranged for conducting electric cur- 

 rents may also be desirable. They will be described in the 

 chapter on the Blood. 



The following substances that cannot be contained in a box, 

 and are necessary in some forms of microscopic work, may be 

 mentioned: osmic acid (1 percent.), nitric acid (C. P.), distilled 

 water, olive oil, caustic soda or potash, chloride of gold ( per 

 cent, sol.).' 



It is also very convenient to have at hand a short wooden 

 rule which is divided into inches and tenths of an inch. The 

 stage micrometer is also equally necessary. Other accessory 

 materials will be described in their proper places. 



HOW TO USE THE MICROSCOPE. 1 



Illumination. When the instrument is ready for use it 

 should be placed upon a firm and rather low table, near a 

 window, which does not receive the direct rays of the sun. If 

 daylight is not to be obtained, a small kerosene hand-lamp will 

 answer sufficiently well for illuminating purposes. The flame 

 should be on a level with the reflecting mirror of the micro- 

 scope, and quite near it. Sometimes a condenser is interposed, 

 but this is rarely necessary, and, indeed, it may be said that it 

 never comes into use in histological work. 



A thin sheet of blue glass may sometimes be found to assist 

 the eye when artificial illumination is used, as the light is made 

 white. Some microscope makers furnish with their instru- 

 ments a set of blue glasses varying in color from very light to 

 dark blue. They are rarely needed, as the eye soon becomes 

 accustomed to continuous work for long sittings, even when 

 strong light is employed. Those who work much with the 

 microscope keep both eyes open, and- use first one and then 



1 Formula in the chapter on General Methods. 



1 It is presumed that students engaging in histological work are more or less 

 familiar with the mechanism of the microscope. For this reason the subject of 

 optical principles and the description of the different parts of a microscope are omitted 

 here. Those who may wish special information on these points are referred to Ap- 

 pendix A. 



