240 THE MICROSCOPE. 



successive section required. One entire revolution of 

 it produces a section T ^ of an inch in thickness, the 

 screw-head being divided into sixths ; thus one division 

 gives a section of ^-^ of an inch, but even thinner sec- 

 tions can be cut by turning the screw. Substances 

 that have been previously prepared in spirit or chromic 

 acid should be steeped in syrup for 24 hours, otherwise 

 they will not readily congeal. It is advisable to cover 

 the apparatus with baize, to facilitate the freezing 

 process. The brass cup (shown in the engraving) is 

 used for holding substances embedded in cocoa-butter, 

 or paraffin ; it also serves for securing hard wood, &c., 

 when cements or sealing-wax are used. 



Vegetable Tissues. Sections of wood and vegetable 

 tissues are susceptible of very fine double and even triple 

 .staining dyes ; the best are atlas-scarlet, soluble blue, 

 iodine, and malachite-green. Mr. Richardson secured 

 success by steeping sections in spirits of wine for 

 about a fortnight, and when not required for immediate 

 investigation, storing them away in Price's glycerine for 

 at least a couple of months. This renders them less 

 liable to fold or break than when the staining is done 

 immediately after the sections are cut. His method 

 may be gathered from the following directions for pre- 

 paring and staining sections of palm stem. After the 

 sections are cut they should be bottled up in a toler- 

 ably dark solution of atlas-scarlet and spirit of wine. 

 Leave them in this solution, corked up tightly until 

 they become of a uniform scarlet tint. Like sections 

 of animal tissues, however, they may remain in the 

 solution for many weeks without risk of spoiling or 

 counteracting the energy of the green dyes. It is on 

 the whole better to complete the process when the sec- 

 tions seein to be of a deep scarlet colour. Remove 

 them and wash them well in filtered water, repeatedly 

 change the water until it ceases to be in the slightest 

 degree coloured by the sections. Then transfer them 

 to a white porcelain water, containing a solution of 

 spirit of wine, coloured bluish-green by adding a couple 

 of drops of an aqueous saturated solution of the green 

 dyes ; a drop of each will be found sufficient. When 



