336 SUilMAKY OF CURRENT RESEARCHES RELATING TO 



blade touches upon one of the two tangential sides and finally reaches the 

 opposing angle. "When the knife is placed across or in front the section- 

 stretcher is usually superfluous, and the block must have the shape given 

 above (under Xo, 1). The handle i serves to remove the rod for cleaning 

 it or the knife-surface, 



(3) The ohjeci-carrier. — The hollow cylinder {1-, fig. 89) serves for the 

 reception of the object to be cut. For this purpose it is filled with 

 hard paraflin ; in this last the paraffin block, in which the object is im- 

 be.hled in the usual way, is melted with hot needles. The cylinder, by the 

 aid of the small pin n (fig, 87), which fits the holes, is capable of vertical 

 and horizontal movement, and is fixed by means of the screw m ; by the 

 milled head n the direction may be altered to the extent of 90^, and the 

 metal frame can receive through the milled head n a similar inclination to 

 the plane standing vertically to it. In this way the object may be placed 

 in any desired direction to the knife-edge. The two levers q and r serve 

 to fix it. Too strong pressure should be avoided, as the plates may be bent 

 thereby, 



(4) The micrometer-screw. — The object-carrier can be moved along by 

 the hand, and for the accurate estimation of the amount of movement 

 there is a vernier which corresponds with the millimetre scale on the 

 vertical upright of the microtome. It is, however, safer to use the micro- 

 meter-screw (fig. 87) the point of which works against an agate. The 

 screw is so threaded that one turn moves the carrier up • 3 mm., conse- 

 quently an upward movement of 1 : 20 produces an ascent of the object of 

 about O-Olo mm. The screw-head is divided into fifteen parts, and there- 

 fore the interspace between any two divisions corresponds to an elevation 

 of 0-001 mm. If by means of the pin u the movable half of the cylinder 

 be shifted so that the numbers Y, X, XV can be read, a click, produced by 

 a spring, will be heard fifteen times at every revolution of the screw. If 

 the two numbers 8 on the side of the cylinder be approximated, the 

 clicking only occurs thrice ; therefore each one corresponds to a raising of 

 the object 0-005 mm. Similarly for 2 and 2 or 1 and 1, the values 0-0075 

 and 0-015 mm. are obtained. The spring-catch arrangement maybe dis- 

 pensed with by raising the handle v. The screw-carrier is fixed to the 

 groove by the milled-head ic. 



Apparatus for controlling the position of the Microtome Knife.* — 

 Dr. T. V. Demboivski's contrivance consists of two distinct parts. In the first 

 of these the knife a (fig. 90) is fixed by the ball-and-socket joint A, the ball 

 of which lies in a hollow excavated in the upper surface of the slide. The 

 arch B covering the ball is fixed by the screws c and D. From above B 

 projects a short tube E, which forms part of the ball. Inside the tube E is 

 a binding-screw, accessible through the opening ; another, h, is seen at the 

 side. Fitting over E, and fixed by the screw G, is another tube F, with 

 two arms H and J. At the end of H is a scale K, and at the end of J a 

 pointer L ; the latter is at right angles to K. Encircling the excavation in 

 the slide is a wall-like ring, about which the plate M turns ; at the end of 

 this plate is a pointer P. The other end of M carries a vertically placed 

 plate Q, provided with a scale. The end of the pointer P is distant about 

 90^^ from Q, so that when the pointer P touches the scale K the point L is 

 brought into contact with the plate Q. The pointer O indicates on the 

 scale X what angle the edge must form with the middle plane of the 

 microtome in order to be able to cut objects of given size when using the 

 whole length of the blade. 



* Zeitschr. f. Wiss. Mikr., ui. (1886) pp. 337-45 (2 figa.). 



