xl INTRODUCTION. 



which will solidify shortly after the gum has frozen. It is advisable to cover the apparatus 

 with baize, to facilitate the freezing process. The edge of the razor must be elevated to the 

 required height for cutting the section by means of the three screws supporting the frame. 

 After the first cut, each end of the razor must be again presented to the surface of the 

 specimen, when either end of the blade can be adjusted by one of the back screws until its 

 entire length is level ; then by turning the large screw in the front part of the frame it can be 

 lowered for each successive section required. 



Preparation of the Material for Freezing. Follow exactly the same methods as are in- 

 dicated at p. xxxviii. A piece of tissue, a quarter of an inch in thickness, is quite sufficient 

 to freeze at one time. The tissue to be frozen is, after the above preparation, placed on one 

 of the circular plates, and is fixed to it with gum solution. The razor ought to be moistened 

 with the same solution, which prevents the sections from curling up. 



TREATMENT OF THE SECTIONS. 



From the bowl of water, into which they are put at first, they are transferred to a conical 

 glass filled with water, in which they gradually subside. All the gum must be got rid of, which 

 is accomplished by changing the water several times. When all the gum is dissolved, transfer 

 the sections to one or other of the following fluids till they are required. Keep them in glass- 

 stoppered bottles. 



PRESERVATIVE FLUIDS. 



1. Ordinary methylated spirit. 



2. Glycerine I oz., water i oz., carbolic acid 4 minims. 



DR. BEVAN LEWIS'S ETHER FREEZING MICROTOME. 



It is not always possible to obtain ice for freezing, and hence it is necessary to have 

 another medium for freezing. This is supplied in the most perfect form by the above in- 

 strument (fig. 21), devised by Dr. Bevan Lewis, of the West Riding Asylum. This microtome 

 is specially valuable for rapid freezing. 



The lower half or body of the instrument (a) is a slightly modified Stirling microtome ; 

 the upper part (b) consists of a freezing-chamber and a section-plate. 



The Body The framework of the body (a) is a solid brass casting, which can be secured 

 to a table firmly by the coarse screw (;). Through its central aperture works the brass plug 

 (/*), driven by a spring and fine micrometer screw (), the pitch being fifty threads to the inch, 

 the screw having a diameter of ^ths of an inch with a milled head i-^ inches across. 



Section-Plate. The section-plate (c] is a circular plate of zinc f ths of an inch thick, raised 

 upon a strongly vertical arm of brass or zinc preferably of the latter metal. In the section- 

 plate there is a circular central aperture through which the freezing-chamber works. Lately 

 the efficiency of the instrument has been much improved by capping the zinc plate (c) with a 

 square of plate-glass ^-inch thick, extra polished and drilled with a central aperture () corre- 

 sponding in size to that in the zinc plate, and which in my own instrument measures 21 inches 

 in diameter. For cutting sections of frozen tissue, the glass-section plate is a great advantage, 

 and when once used will never be dispensed with. It renders the movements of the knife 

 absolutely free and easy, whilst, on the other hand, the blade never gets injured from scratches 

 which sooner or later invariably appear upon a metal section-plate, and which turn or indent 

 the edge. 



