204 



The Microscope. 



necessary thickness, and 

 over them the ends a 

 little wider than the 

 sides. On opening the 

 card a small square will 

 be seen at each corner 

 marked out by the folds. 

 /I ^ Now bring the end fold 



of one of these squares exactly against the side fold of the same 

 square and draw the intermediate paper (A, b) between the 

 thumb and linger, which divides each square into two triangles. 

 Turn the triangle over the end of the cell and repeat on the other 

 side. A complete end is thus formed to the cell. To hold the 

 triangles in place and keep the end from unfolding, turn the top of 

 the end paper, which projects a little above the level of the sides, 

 over. (A, 2, a.) Prepare the other end of the cell in the same 

 manner. It is necessary that the folds at the corners meet exactly, 

 or the cell will be irregular in shape. 



I^^~""~" A very good cell-form may be made by bending rather 

 I thick pieces of lead, so that the two sides are at right 

 ■"^■""^ angles to each other. For embryos, however, the paper 

 cell is preferable. 



SECTION IV. 



SECTION CUTTING — PREPARATION OF SLIDES MOUNTING. 



§ 11. The embryo, embedded as given in § 9, A, is ready for 

 cutting. As the sections must be serial and laid upon the slide in 

 I'egular order, so that the organs and parts may be studied with 

 exactness, it is necessary that a sufficient number of glass slides be 

 in readiness.* These must be perfectly clean and clear. Each 

 slide in turn should be warmed over the sj)irit lamp flame, and when 

 the moisture, which collects on the application of the heat, disap- 

 pears, a glass rod dipped in the shellac solution (already mentioned) 

 must be pushed over the slide in such a way as to leave behind it a 

 thin film of the shellac. This may easiest be accomplished by 

 running the rod across the glass, and then quickly drawing it over 

 the length of the slide. It is not necessary, however, that over an 

 inch of the surface should be covered by the shellac. If the film 

 left turns opaque, it indicates that the glass was not hot enough, and 

 in that condition is unfit for use. The film should be perfectly 



* The size of the slide used is quite immaterial. Those which I have found most 

 convenient for this purpose measure two inches by one and a fourth inch (Heidelberg form.) 



