6 INTRODUCTION. 



relation to life habits, without the use of special instru- 

 ments and reagents. The latter things are to be called 

 into use to extend the vision beyond its ordinary limits- 

 If this fact is not kept constantly in mind, the study may 

 easily resolve itself into the mere manipulation of labora- 

 tory tools, or a study of the technique of instruments 

 and reagents. A knowledge of these things is helpful to 

 a high degree when their proper use is clearly defined. 



Do not dissect specimens or make sections until it is 

 decided in a general way what to look for and where to 

 look for it. Such a general notion is essential to proper 

 orientation of structures. 



When specimens are to be mounted one must be care- 

 ful lest they become dry by evaporation. Water may 

 easily be placed upon a drying specimen that has been 

 mounted, by touching a wet brush or a drop of water 

 from a pipette at the edge of the cover-slip. 



Many of the materials for study may be mounted 

 entire. Others will need careful dissection by use of the 

 needles. This dissection will often be made much more 

 easy and far more successful by first boiling the material 

 for one or two minutes in a five per cent solution of potas- 

 sium hydroxid, then pouring off the liquid and rinsing in 

 water. Still others can be studied only by means of care- 

 fully made sections. Some of these sections should be 

 made by use of the microtome, but most of them the 

 student can make by free-hand cutting with a good razor. 

 Very delicate materials may be sectioned by being placed 

 between pieces of pith. More rigid ones may be held free 

 in the hand, or in the hand-microtome. 1 



1 For methods of killing, imbedding, sectioning, staining, and mounting 



