MEASUREMENT OF OBJECTS 



especially when the high power has been used : in this case 

 the tube should first be raised so as to remove the objective 

 from close proximity to the stage, and the slide should then be 

 slipped off the stage^ not lifted off. Want of attention to these 

 points is apt to result in smearing the objective with glycerine, 

 or other media. 



Drawing from the Microscope. Nothing compels attention 

 to details of an object so successfully as drawing it ; while, as 

 it is impossible to make a drawing of an ill-prepared object, 

 the intention to make a drawing will have its effect upon the 

 care devoted to preparation and mounting. It should be a rule 

 for students to draw every object they observe^ not merely for the 

 sake of the drawings as memoranda, but in order to acquire a 

 habit of close observation. 



For drawing, a hard pencil (H.H.H.) is recommended, and it 

 must be cut to a fine point : paper with a hard smooth surface 

 is to be used, or better, a thin drawing card or Bristol board 

 with a hard surface. A decisive style of drawing should be 

 adopted, in which every line is clear, and conveys its own 

 meaning. 



For ordinary purposes a freehand drawing will suffice, the 

 scale being as nearly as possible that of the object as it appears 

 under the microscope, or larger, if the object be a complicated 

 one : whatever the scale, the proportion of the several parts is 

 to be scrupulously followed. Coloured chalks, or better, light 

 washes of water-colour, may be used for distinguishing tissues 

 of different character, and in making a series of drawings 

 the same colours should be assigned to corresponding tissues 

 throughout the series. 



When drawing cell-walls of appreciable thickness, they 

 should be indicated by a double line ; solid bodies should be 

 shaded so as to give the idea of light coming from one side, 

 and in a series of drawings the side selected should be main- 

 tained throughout. 



Measurement of Objects. Measurements may be most 

 readily made by means of an eye-piece micrometer, which is a 

 glass slip, fitted into the eye-piece, and having a scale engraved 

 upon it. The value of the divisions of this scale varies with 



