xxvi INTRODUCTION. 



Measure an ounce of No. i cover-glasses, and put aside all those under -004 inch for 

 use with high powers. 



(b) The cover-glass measurer (Deckglass-taster) of Zeiss (fig. 9) is a very convenient appa- 

 ratus, which has a movable disc, d, divided into degrees. The cover-glass, c, is placed between 

 the ends of two screws, and the disc is rotated till the screw just holds the cover. By an 

 ingenious arrangement of teeth the handle is thrown ' out of gear ' when this occurs. It gives 

 the thickness of a cover-glass in parts of a millimetre. 



HOW TO PLACE A SECTION ON A SLIDE. 



The section ought to be placed in a bowl of water preferably a white bowl as it admits 

 of the section being easily seen. Take a slide, and plunge it for three-quarters of its length 

 into the water, and with a needle in the right hand gently guide the section on to the slide, 

 which ought to be held in a slanting direction. The section is thus easily floated on to the 

 slide, and thus all unnecessary tearing of it is avoided. The needle is used to hold the section 

 on the slide whilst the latter is being removed from the water. Remove the surplus water 

 with a towel. To the section on the slide the necessary staining reagents may be applied. 

 Sections may easily be treated with alcohol and clove oil on a slide. This method is 

 infinitely preferable to lifting sections from clove oil, etc., even with the most approved form 

 of ' section-lifters.' 



LABELLING OF MICROSCOPIC OBJECTS. 



This is most important. Every preparation, when mounted, ought to be properly labelled. 

 Small paper labels are affixed to the slide, and on these are marked the nature of the section, 

 whether it is a transverse (T. S.) or a longitudinal section (L. S.) ; any special points in its struc- 

 ture ; how it was prepared and in what medium it is mounted. The thickness of the cover- 

 glass in special cases ought to be indicated. By using a series of symbols, as PC for 

 picrocarmine, Lg for logwood, G for glycerine, D for dammar, and F for Farrant's solution, 

 much important information can be put upon one small piece of paper. 



ON MAKING DRAWINGS OF MICROSCOPIC 

 PREPARATIONS. 



It is of the utmost importance that each student should make a sketch of many, not neces- 

 sarily of all, the preparations he mounts. This is the only method of ensuring that he sees 

 what is to be seen. The outline plates are designed to aid the student in this task. Once the 

 student has made a drawing of the details of a preparation he is not likely to forget them. It is 

 far more important that each student should thoroughly understand a selected series of pre- 

 parations than that he should carry off with him a couple of hundred slides, few of which he 

 understands. 



Various instruments are used for making drawings of microscopic preparations, but it is to 

 be remembered that they are in many cases more useful for giving the actual size of an object 

 as seen with a certain combination of lenses, and for giving the general outline of a section, 

 than for the individual details. 



