ZOOLOGY AND BOTANY, MIGROSCOPY, ETC. 



32i 



the flat, it is more efficient for three reasons : It is more rigid, it gives 

 a better clearance for the microtome knife, and it contains less material. 



In the case of small and moderate sized objects of which only a 

 few sections are reqnired, the method is extraordinarily expeditious. 

 Objects of such a size that they can be embedded in a few drops of the 

 freezing mixture placed on the control part of either of these metal 

 supports can be frozen in a few seconds by applying an ordinary ether 

 spray to the under side of one of these thin metal supports. The 

 exceeding rapidity of the congelation gives rise to a consistency favour- 

 able to section cutting. 



To obtain an End Vieic of a Nema, Rotifer, or other similar Small 

 Object. — Suppose the object is a nema of which an end view of the head 

 is required : decapitate the nema behind the pharynx with the aid of 

 an eye knife, or similar very small tool having a very slender, thin blade. 



Fig. 3. — Perspective view aud lougitudinal section of a freezing- 

 microtome object-holder mounted on a cork cylinder. The holder 

 is made of metal only about two thousandths of an inch thick. The 

 edges of the ring (r) are beveUed so that the embedding mixture 

 when frozen is dovetailed to the holder. 



The smallest and most slender-bladed knife used by oculists in opera- 

 tions on the eye is a very suitable tool, and it must have the degree of 

 sharpness characteristic of surgical instruments in good order. Bring 

 the nema by appropriate methods into glycerine ; the decapitation 

 should be done in a drop of glycerine placed on the surface of a trans- 

 parent piece of celluloid. Push the nema to the bottom of the glycerine 

 and against the celluloid ; decapitate by pressing the edge of the knife 

 against the nema as the latter rests on the celluloid. The celluloid is 

 sufficiently soft so that the edge of the knife will not be dulled. If the 

 knife is sharp, the cut will lie clean, and the object satisfactory. If 

 the knife is dull, the nema will be more or less crushed at the point of 

 section and the preparation may prove unsatisfactory. 



Mount the head in melted glycerine jelly, using sufficient jelly so 

 that the object may stand on end after being covered in. Place the 



