12 SECTION CUTTING 



the specimen in some waxy substance. For this purpose various 

 materials have been employed, but by far the most useful is 

 paraffin-wax, which is used in the following manner : 



The stained specimen is placed in absolute alcohol for an 

 hour or two in order to completely dehydrate it. It is then 

 transferred to turpentine or benzole, in which it is left for half 

 an hour or more until completely saturated. From the tur- 

 pentine or benzole it is transferred to melted paraffin, which is 

 kept by means of a water-bath at a temperature just above 

 its melting-point (about 56 C.). In this it is left for several 

 hours, or even for a whole day, in order that it may be 

 thoroughly permeated. It is then placed in a small box of 

 paper, or other material, filled with melted paraffin. By means 

 of hot needles it can readily be arranged in any desired posi- 

 tion ; and the paraffin should then be cooled quickly. 



D. Section Cutting. 



When thoroughly set the block is removed from the box, and 

 the paraffin pared away with a knife until the specimen just 

 comes into view. 



The block is then placed in a microtome, and cut into thin 

 sections. These may be transferred one by one to a slide, but 

 a great saving of time is effected by the method of cutting 

 continuous ribbons, devised by Mr. Caldwell. 



This depends on the fact that if the paraffin is of proper 

 consistency the successive sections, as they are cut, will stick 

 together at their edges, so as to form a ribbon. To ensure this 

 the edge of the razor should be placed at right angles to the 

 direction of stroke, and the edges of the block of paraffin cut 

 parallel to one another, and to the edge of the razor. If for 

 any reason it is desirable to imbed the specimens in a paraffin 

 too hard to form ribbons, the block should, before cutting, be 

 coated with a layer of soft paraffin, by dipping it for a few 

 moments in a dish of melted soft paraffin. This outer coating 

 should be left on the sides of the block parallel to the edge of 

 the razor, but cut away from the sides at right angles to it. 



The razor should be used dry : and the sections, when cut, 

 placed on slides painted, just before they are used, with a thin 

 layer of a mixture of collodion and oil of cloves in equal parts. 

 The slide is then heated by a water-bath to a temperature not 

 exceeding 55 to GO C., so as to melt the paraffin and evaporate 



