ON CUTTING SECTIONS. xxxi 



to objects washed after fixing. Treat subsequently with 

 50 per cent., 70 per cent., and acid-alcohol. 



Hematoxylin (especially Meyer's acid-hsem-alum, see 

 Appendix) gives excellent results if used with due care, but 

 a trace of acid or turpentine will completely -destroy the 

 colour. 



X. ON CUTTING SECTIONS. 



Many points in anatomy and histology may be best made 

 out by examination of microscopical sections that is, slices 

 cut so thin as to allow of their being examined under the 

 microscope by transmitted light. 



The hardened object, supported, if necessary, between 

 two pieces of carrot, may be held between the fingers and 

 thumb, and sections sliced off it freehand with a sharp 

 razor. 



The microtome or section-cutting machine, however, gives 

 better results. It consists essentially of three parts : a clamp 

 or other contrivance for holding the object to be cut, means 

 of guiding the razor, and a ' feeding ' arrangement. These 

 parts are so arranged that the razor can be drawn smoothly 

 across the object to be cut, taking off a section at each stroke, 

 the ' feeding ' arrangement bringing the object into the path 

 of the razor, and the amount of ' feed ' determining the thick- 

 ness of the section. 



In the simplest form of microtome the razor is drawn by 

 hand over a smooth plate, the object to be cut being pushed 

 up through a hole in the centre of the plate by means of a 

 screw or other ' feeding ' arrangement placed below. 



More complicated microtomes have been devised to obviate 

 the wearing of the edge of the razor by friction upon the 

 plate ; to render it possible to cut the object in any desired 

 direction ; to cut more evenly, more easily, and more rapidly ; 

 and to yield sections in a string or ribbon, so as to simplify 

 and expedite the mounting of large series of sections. 



The preparation of an object for cutting in a microtome 

 depends to some extent upon the nature of the object and 



