14 THE ELEMENTS OF VEGETABLE HISTOLOGY 



be accurately trimmed so that the opposite sides are 

 parallel, and the knife kept warm during the operation. 

 Rotary machines give better ribbons than sliding 

 microtomes. In cold weather very good results may 

 be obtained by placing the machine on a radiator. 

 After the first few sections have been cut, they should 

 be gently drawn away from the knife and attached 

 to a revolving drum (Fig. 7) so that the entire series 

 may be kept intact. Curling of sections may be 

 partially overcome by warming the block, as this 

 fault is usually the result of using hard paraffin. 

 Frictional electricity is occasionally a disturbing 

 element, but this may be overcome by running a ground 

 wire between the machine and a water or gas-pipe. 

 Removal of Embedding Medium. — Unless the 

 sections are to be stained they are now immersed in 

 xylol to dissolve the paraffin. It is best to use two 

 xylol baths, draining the sections after the first immer- 

 sion and using fresh solvent for the second. After 

 being washed in xylol the sections may be mounted 

 in balsam or may be brought into aqueous media by 

 reversing the operations described in the section on 

 Dehydration. If the sections are to be stained, and 

 particularly if one is working with serial or ribbon 

 sections, each section with the adhering paraffin is 

 laid flat upon a clean slide previously prepared so that 

 the sections will adhere. Slides for this purpose are 

 coated with a mixture of egg albumin and glycerin 

 (1 : 1) and then dried at a moderate temperature. 

 Just previous to use, the albuminous film is moistened 

 with water. The prepared slide with the specimens 

 properly arranged is placed upon a warm plate or in 

 a low temperature oven and gently heated so that 



