12 ON SECTION CUTTING. 



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 position ; and the paraffin should then be cooled 

 quickly. 



E. 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 moment 

 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° — 60° C, so as to melt the paraffin and evaporate 

 the oil of cloves. The melted paraffin should then be washed 

 off by turpentine, w^hen the sections will remain fixed to the 

 slide by the collodion, and may be mounted in balsam in the 

 usual manner. 



Instead of the mixture of collodion and oil of cloves, a solution 

 of shellac in absolute alcohol may be used : this should be 

 spread over the slide in a thin layer by means of a glass rod, 

 and allowed to dry. Immediately before being used the slide 

 should be brushed over with oil of cloves. 



