778 SUMMARY OF CURRENT RESEARCHES RELATING TO 



methods of sharpening them. Under the first heading he describes the 

 bevels and the effects of notches and striae upon the sections cut. 

 The fluting and opacity of the free portion of paraffin sections illustrates 

 the effect of these striaa ; with a perfect edge the paraffin should cut 

 quite clear. Under the second heading he considers the materials used 

 for sharpening razors, and emphasizes the necessity of using fine impalp- 

 able powders of uniformly sized grains. The uniformity of these grains 

 is secured by making timed suspensions in water. He recommends the 

 use of alumina. Finally, he describes apparatus in which the manual 

 labour is replaced by water-driven or electrically-driven sharpening 

 machines. 



Large Sliding Microtome.* — The Cambridge Scientific Instrument 

 Company has recently designed a large microtome (PL XV. figs. 2, 3) for 

 cutting flat sections up to 150 x 120 mm. (6" x 4f"). It is capable of 

 cutting through decalcified bone or cartilage, and is being found ex- 

 tremely useful for cutting sections which are too large to be cut with 

 either of the makers 1 two rocking microtomes. 



The object, embedded in a block A of paraffin wax or celloidin, is 

 fixed to the wood block which is clamped in the object-holder B. This 

 object-holder is fitted with orientating adjustments very similar to those 

 used in the makers' rocking microtomes ; being mounted in a cup-shaped 

 socket at the end of a brass pillar E. This pillar can be raised or lowered 

 and clamped at any height by the clamping screw D. The orientating 

 adjustments are made by four screws, one of which is lettered C. 



The sliding carriage, which supports the object-holder and feeding 

 mechanism, rests at three points on two guides in the frame of the 

 instrument. The whole carriage can be moved backwards and forwards 

 on these guides by means of the handle G, working through the levers H. 

 The design is such that all wear is automatically compensated for. After 

 the cutting stroke, and when the carriage has nearly reached the extreme 

 position as in fig. 1, a stop-pin, operating through the ratchet M, turns 

 the toothed wheel L and screw K, so feeding the object-holder upwards. 

 The amount of the feed is regulated and indicated by the index P. On 

 the return stroke the mechanism causes that part of the sliding carriage 

 which holds the object-holder to drop just before it reaches the knife R, 

 in order to avoid fouling the same, and to rise after passing the knife to 

 its former position in preparation for the next cutting stroke. 



The construction of the sliding carriage is such as to convert the feed 

 into a parallel motion, and so give sections of a uniform thickness ; and, 

 further, since the carriage slides on plane guides, the sections are also 

 from a plane surface. The knife R, is clamped in two heavy brass clangs 

 by the screws SS. The position of these clamps can be moved so as to 

 set the knife obliquely to the direction of movement of the object. The 

 clamping screws TT hold the clamps firmly in position. The angle the 

 cutting edge makes with the horizontal plane is also readily adjustable, 

 and a small angular scale is divided on the knife-holders so that the same 

 angle can be easily repeated. 



Two knives, each measuring 80 cm. long by 5 cm. wide, are supplied. 

 The first one "A" is grouud to a very fine angle, and is used for delicate 



* Cambridge Scientific Instrument Co., List No. 57a (1910) pp. 8-10 (3 figs.). 



