182 The Microscope. 



which the holder is filled, by means of a heated wire, is covered with 

 a thin coat of soft paraffine or " paraffine-gum," and of which *' chew- 

 ing-gum " * is made. This enables one to cut ribbons of any 

 desired length, since the softer paraffine at the edges of the suc- 

 cessive sections sticks them together by their margins as fast as they 

 are cut. 



The ribbons may be allowed to fall upon a slip of paper, which 

 may be drawn out, as fast as the sections are cut, from under the 

 bed-plate of the instrument, beneath which there is a space left for 

 this purpose between the three toes or tripod upon which the whole 

 apparatus rests. The edge of the knife also remains in the same 

 plane, no matter at what angle the cutting-edge is placed with refer- 

 ence to the direction in which the block to be cut is moved, just as 

 in the best forms of the sledge microtome. Prof. Ryder writes us 

 that in order to control the cutting and keep the sections from curl- 

 ing, a camel's-hair pencil may be held close to the blade. This 

 is found to answer ordinarily, but later experience has shown that it 

 is possible to attach a section-flattener in the form of a roller of 

 hard rubber, which turns loosely on a rod held parallel with the 

 knife edge. The roller is placed with its center somewhat in 

 advance of the knife edge, the rod supporting it may be fastened to 

 the back edge of the knife or be clamped in the position of the sup- 

 port which holds the tube conveying the alcohol to the knife when 

 cutting celloidin sections. 



In cutting celloidin or collodion masses, it has been found that 

 the greater the inclination of the knife the better the results, and 

 it may be found expedient to devise a special form of clamp for 

 cutting celloidin. For paraffine cutting, this instniment has no 

 equal for practical efficiency. 



A new, paraffine bath, which has also lately been devised by 

 Prof. Ryder, promises to become an important aid in embedding. 

 This new device does away with the ordinary form of water-bath as 

 used at Naples ; it also does away with the need of a thermostat, the 

 paraffine itself serving to indicate the place where it is safe to place 

 an object to be embedded. A description with a figure of this new 

 device will appear in the May number of the American Naturalist. 



The advantages which this new instrument offers, are, briefly, 

 comparatively small cost, great efficiency, rapidity, and accuracy. 

 One hundred sections per minute may very readily be cut with it. 



* Chewing-gum may be rendered available for this purpose if it is melted at a tempera- 

 ture somewhat above boiling, when the sugar which it contains will separate as caramel, 

 leaving the pure paraffineguni. which may be drained off and used as directed, if the 

 manipulator should find it difficult to get the parafBne-gum of commerce. 



