ZOOLOGY AND BOTANY, MICBOSCOPY, ETC. 685 



first to last. " Cutting up large objects in the manner above described is 

 not possible with any other form of microtome yet constructed." 



Almost any section-knife — wide or narrow-bladed — will fit into and be 

 firmly held by the knife-clamp, which is, however, intended more especi- 

 ally to hold an ordinary razor. 



For ribbon-cutting by the paraffin method, the block containing the 

 object, after it is trimmed and soldered to the parafiin with which the 

 holder is filled, by means of a heated wire, is covered with a thin coat of 

 soft paraf&n or " paraffin-gum," and of which " chewing-gum " is made. 

 (Chewing-gum may be rendered available for this purpose, if it is melted 

 at a temperature somewhat above boiling, when the sugar which it con- 

 tains will separate as caramel, leaving the pure parafiin-gum, which may 

 be drained off and used as directed, if the manipulator should find it 

 difficult to get the paraffin-gum of commerce.) This enables one to cut 

 ribbons of any desired length, since the softer paraffin at the edges of the 

 successive 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 reference to the direction in 

 which the block to be cut is moved, just as in the best forms of the 

 sledge microtome. 



A section flattener can be attached 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 centre somewhat in advance of the knife-edge and the rod 

 supporting it may be fastened to the back edge of the knife or be clamped 

 in the position of the support 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 clasp for cutting celloidin. 



Mall's Section-smoother.* — Dr. P. F. Mall recommends a section- 

 smoother constructed on the following principle. It consists of a rubber 

 rod about 1^ cm. in diameter, which rotates loosely on a solid axis. The 



Fig. 196, Fig. 197. Fig. 198. 



rod is so placed that it hangs a little below and in front of the edge of the 

 knife (fig. 196). When the knife passes over the object, the rod is raised 



* Arch. f. Auat. u. Physiol.— Anat. Abtheil., 1887, pp. 2-3 (3 figs.). Cf. Amcr. 

 Naturalist, xxi. (1887) p. 597 (3 figs.). 



