292 APPENDIX. 



The tissue to be cut is embedded in the brass cylin- 

 der in much the same way as in an ordinary embedding 

 trough. A little of the embedding mass is first poured 

 in ; when this has begun to set the tissue is placed upon 

 it, and the cylinder is then filled up with more embedding 

 mass so that the object is completely inclosed. It is 

 better to use a mixture of paraffin and hog's lard (5 parts 

 paraffin to 1 part lard) as an embedding mass, since the 

 ordinary wax and oil mixture tends in cooling to shrink 

 away from the sides of the tube. 



In cutting the sections the metal plate p serves to 

 direct the razor, so that it moves in a perfectly even plane. 

 By turning the screw .s the plug of embedding mass with 

 the included tissue is caused to project very slightly 

 above the plane of the plate, so that when the razor, wetted 

 as usual with spirit, is carried over this, a section is ob- 

 tained varying in thickness according to the extent to 

 which the screw was turned. In like manner a large 

 number of consecutive slices may be made. But it is 

 doubtful whether, with this or any other microtome, it is 

 possible to get sections as thin as they can be made with 

 the free hand. 



Simple form of microtome for holding in the hand whilst cutting sections. 



iMjnire 88 shows a smnller instrument (Ranvier's), 

 differing from the other one chiefly in the fact that it is 

 held in the hand whilst the sections are cut. in place of 



