CHAPTER I. 

 INTRODUCTORY EXERCISES. 



THE following substances may be accidentally included in 

 a preparation and present subjects upon which a number of 

 operations important in microscopy can be usefully practised. 



Examination and description of an object. As a rule examine 

 first with a low power (L) to gain an insight into the general appear- 

 ance and arrangement of the object, and its apparent size under this 

 magnification. Then employ the high power (//) to study detail. Do 

 not omit to return to the low power occasionally, for the purpose of 

 comparing appearances, and of ascertaining whether details found under 

 the high power are discernible under the lower one. This procedure is 

 of great importance in accustoming the eye to recognise the relative 

 proportions and dimensions of structures. In describing a structure 

 notes should be made under the following headings. Form, general 

 shape, outlines, surfaces under this the nature of any markings should 

 be given. Size, long and short diameters and thickness. Substance, 

 whether uniform (homogeneous), granular, or reticular. Presence of a 

 nucleus or other contents. Colour. Grouping, tendency to cohere. 

 Movement*, general and internal. Effect* of reagents. 



Cotton fibre. Stretch a few fibres across a drop of water 

 on a slide and apply a cover. 



Application of a cover-glass. Always cover the object with a 

 cover-glass before examining it under the high power. Hold the cover 

 between the thumb and forefinger of the left hand, place one edge of it 

 in contact with the mounting fluid, and resting the other on the point of 

 a needle gradually lower the cover so that air bubbles may be carried to 

 one side clear of the object and of the cover. 



Examine with a low power (L), a number of fine filaments are 

 visible, the details of which are better seen with a high power (//). 

 Each fibre is a flattened tube often partially filled with air. The 

 walls are smooth, and the fibre is frequently twisted. 



