THE AIMS AND METHODS OF LABORATORY WORK IX 



BIOLOGY. 



The purpose of all laboratory work is to study nature at first 

 hand. Its educational value lies chiefly in the cultivation of ac- 

 curacy and independence both of observation and of judgment. 

 Each student is expected to make for himself the observations and 

 experiments hereafter indicated. 



A record of every observation or experiment must be entered in 

 the prescribed note book, under numbers corresponding to those 

 in these Directions. This record should consist of drawings and 

 descriptive notes, and every page should bear the name of its 

 author and the date. The record for each topic must be inspected 

 and passed by an instructor before any new topic may be under- 

 taken. 



To each student in the laboratory is assigned a locker containing 

 a microscope, reagents, glassware, etc., for the safe keeping of 

 which he is held responsible. The microscope is the most complex 

 and delicate instrument in this outfit and work with it should be 

 preceded by a study of the following description of its parts and 

 directions as to its use. 



I. THE MICROSCOPE. 



A. DESCRIPTION. The body or tube bears the lenses and is 

 supported upon a stand which also carries a mirror to cast light upon 

 the object examined through a hole in the flat stage upon which the 

 object is placed. This hole can be made of various diameters by 

 means of diaphragms. A lens for concentrating light, and known 

 as a condenser may be placed between the mirror and the stage. 

 The lens at the upper end of the tube is the ocular or eye-piece; 

 there are two oculars, of different magnifying power. The combi- 

 nation of lenses at the lower end of the tube is the ob fee tire; 

 in this microscope there are two objectives of different magnifying 

 power, one marked 3, the other 6; the former ( low power objective) 

 is in focus, i. e., gives a clear image of the object examined when 

 its lower end is about 2 /$ in. above the object, the latter (high power 

 objective) is in focus when it is about l /^ in. above the object. The 

 objectives are carried upon a nose-piece by revolving which either 



