552 SUMMARY OF CURRENT RESEARCHES RELATING TO 



ingou the perfection with which the razor is sharpened, to a maximum 

 of 5/32 of 1/25 of 1/G j or 1/1000 of a tnrn. The practical miuimmu 

 thickness obtainable with a good razor is approximately 1/40,000 in. 

 The value of the teeth on the milled wheel are as follows: — 



1 tooth of the milled wheel = 1/40,000 in. = -000025 mm. 



2 teeth „ „ =1/20,000,, =-001250 „ 

 4 „ „ „ = 1/10.000 „ = -0025 „ 



16 „ „ „ = 1/2500 „ = -01 



The movement of the lever which carries the imbedded object is 

 effected by a string attached to one end of the lever. This string 

 passes under a pulley and is fastened to the arm carrying the pawl. 

 Attached to the other end of the lever is a spring pulling do\^^l wards. 



When the arm is moved forward tlie feed takes place, the string 

 is pnlled, the imbedded object is raised past the razor, and the spring 

 is stretched. When the arm is allowed to move back the spring 

 draws the imbedded object across the edge of the razor, and the 

 section is cut. The string is attached to the lever by a screw which 

 allows the position of the imbedded object to be adjusted so that, at 

 the end of the forward stroke, it is only just past the edge of the 

 razor. This is an important adjustment, as it causes the razor to 

 commence the cut when the object is travelling slowly and produces 

 the most favourable conditions for the sections to adhere to each other. 



The following are perhaps the most prominent advantages of this 

 instrument. (1) The price is one-sixth that of the original form. 

 (2) Less skill is required from the operator, for the endless silk band 

 is superseded, and the troublesome and difficult operation of lifting 

 the first sections from the razor on to the silk band is entirely 

 avoided ; the ribbon of sections now falls of its own weight direct 

 from the razor on to a piece of paper or glass slide placed to receive 

 them, and by occasionally moving the paper forward any length of 

 ribbon can be obtained. (3) The razor is fixed at what has in practice 

 been found the most advantageous inclination and angle for cutting, 

 and thus an unnecessary adjustment and waste of time is avoided. 

 (4) The imbedded object is with great ease and quickness brought 

 up to or away from the edge of the razor ; first for large amounts by 

 sliding backwards or forwards the brass tube on the cast-iron lever, 

 then for t^maller amounts by turning round the screw, when the pawl 

 is out of gear, by means of a small milled head placed on the top for 

 this purpose. (5) There are no delicate working parts which can get 

 out of order, and the whole instrument is easily taken apart for 

 packing and is very portable. 



"Ribbon" Section Cutting.* — Mr. A. B. Lee gives the following 

 as the factors necessary for the production of a chain of sections : — 



First, the paraffin must be at a melting-point having a certain 

 relation to the temperature of the laboratory. Insufficient experi- 

 ments have yet been made to settle the melting-point of the 2)araffins 

 that should be used at the different temperatjLires at which sections 



♦ ' The Microtomist'ri Yale Mecum,' 1885, pp. 400-1. 



