86 



Journal of Applied Microscopy. 



attached to a slide F, which may be 

 elevated or lowered by a feed, G, which 

 consists of a micrometer screw acting 

 on the lower surface of the slide. The 

 micrometer screw is provided with a 

 milled head, divided into a definite num- 

 ber of parts which bear a definite rela- 

 tion to the pitch of the micrometer 

 screw. 



The instrument shown in the figure is 

 further provided with a lever H, which 

 may be so adjusted as to move the 

 milled head on the micrometer screw one, 

 or any desired number of notches at 

 each movement of the lever; and as each 

 notch on the milled head has a value of 

 5 microms (1-5000 of an inch), every 

 time the milled head is moved one notch 



filtered kerosene oil. While sharpening 

 the knife it is grasped with both hands, 

 with one by the handle, with the other 

 by the end. The hone is placed on a 

 table with one end directed toward the 

 person sharpening. If the knife is very 

 dull, it is ground for some time on the 

 concave side only (all microtome knives 

 are practically plane on one side and 

 concave on the other), with the knife 

 at right angles to the stone. It is car- 

 ried from one end of the stone to the 

 other, edge foremost, giving it at the 

 same time a diagonal movement, so 

 that with each sweep the entire edge 

 is touched (see Fig. 2). In drawing back 

 the knife, the edge is slightly raised. 

 The knife is ground on the concave side 



Fig. 1. 



(toward the manipulator), the slide car- 

 rying the clamp holding the tissue is 

 elevated 5 microms; two notches would 

 elevate the tissue 10 microms (1-2500 of 

 an inch); four notches, 20 microms 

 (1-1250 of an inch), etc. It is not essen- 

 tial to have a lever, as above described, 

 attached to the instrument, although this 

 is very convenient, in which case the 

 milled head is moved the desired num- 

 ber of notches with the hand. 



Microtome Knife. — No matter how 

 well the tissues may be hardened and 

 imbedded, and no matter how good the 

 microtome may be, unless one has a 

 good and sharp microtome knife, good 

 sections cannot be cut. To be able to 

 sharpen a microtome knife is therefore 

 very essential unless one wishes to send 

 the knife to an instrument maker every 

 little while. For this purpose I use a 

 Belgian hone and moisten or lubricate 

 the same, while grinding the knife, with 



until a fine thread (feather edge) 

 appears along the entire edge. It is then 

 ground on both sides, care being taken 

 to keep the knife at right angles to the 

 stone, to keep it flat on the stone and 

 to use practically no pressure at all. It 

 is a good plan to turn the knife, when 

 the end of the stone is reached, on its 

 back. On the return stroke, the knife 

 is again held at right angles to the 

 stone, the same diagonal sweep is used 

 (see Fig. 2), so that the whole edge of 

 the knife is touched with each sweep 

 of the knife. The grinding on both sides 

 is continued until the thread above men- 

 tioned has disappeared. The knife 

 should now be carefully cleaned and 

 stropped, with the back of the knife 

 toward the strop. The strop should be 

 flat and rest on a firm surface. After 

 stropping, the knife should cut a hair 

 held between the fingers, but the best 

 test for the knife is, after all, that of 

 cutting sections. 



