INTRODUCTION. 



XXXIX 



MODIFICATIONS OF THE ABOVE METHOD. 



In tlie preparation of the Tissues (a). For some tissues e.g. brain it is necessary to leave 

 them forty-eight hours in the gum before cutting. 



(b) The following method is an excellent one, and is of the greatest value for very delicate 

 tissues as the retina, ear, brain. After soaking the tissues in water, place them for twenty- 

 four hours in syrup made by dissolving four ounces of crystallised sugar in two ounces of 

 water. They are afterwards placed in gum for twenty-four hours, and are then ready for 

 cutting. 



With such a microtome as described above there is no difficulty whatsoever in making the 

 most perfect sections. The well can be made of any size, and, indeed, D. J. Hamilton, of 

 Edinburgh, has had a large freezing microtome constructed which enables him to make 

 microscopic sections of an entire brain. 



WILLIAMS FREEZING MICROTOME. 



Some histologists prefer this form of microtome (fig. 20). It is made by Swift, of London, 

 and consists of a wooden tub for the freezing mixture. In this is an upright, brass bar, into 

 whose upper end the circular brass plates, on which the tissue is frozen, are screwed. A glass 

 top with a hole in its centre, through which the circular plate projects, forms a lid for the box. 

 The knife is fixed in a triangular frame, provided with screws by which it can be raised or 

 lowered. 



METHOD OF USING WILLIAMS' MICROTOME. 



Remove the lid of the box and fill the chamber with equal parts of pulverised ice and salt, 

 care being taken not to allow the mixture to touch the under side of the cover, which, when 



Fig. 20. WILLIAMS' (QUECKET CLUB) FREEZING MICROTOME. 



replaced, must be firmly secured by the clamp screw for that purpose. The substance to 

 be cut is placed on the surface of the central circular brass piece, and surrounded with a 

 solution of gum, which readily congeals, and will thus hold the specimen firmly in position, 



