44 CORRESPONDENCE. 



permission to ask him for iuformation as to what tissues were 

 examined, their thickness, how prepared, in what media mounted, 

 what structures were seen in them, how defined, and to what depth 

 were they well seen ? 



If Mr. Hickie will be so good as to inform us upon these points, 

 and any others that may occur to him, I am sure he will confer a 

 favour upon all who, like myself, are looking forward anxiously to 

 improvements in physiological glasses. 



I am, Sir, faithfully yours, 



E. Bran WELL. 



A New Section Blade. 



To the Editor of the ' Monthly Microscopical Jourmd.^ 



Baltimore, Md., November 14, 1875. 



Sib, — The qualities required in a section useful for microscopic 

 research are even thinness pushed as far as tissue structure demands, 

 and smooth surfaces, the production of a perfect knife edge. This 

 last is urged forward in slicing fashion, whether a holder be employed 

 or not; but in all cases personal equation varies or jeopardizes the 

 result, and the student's end can be attained then only when this 

 element ui failure or inconstancy shall have been minimized. 



Wherefore it occurred to me to have recourse to an excentric 

 knife, and I devised in the month of June last the blade which I 

 employ. It resembles the chisel of a plane, but its edge forms the 

 arc of a circle of 2^ inches radius, of whicli the centre is above and to 

 the left of the axis of revolution ; consequently it works excen- 

 trically in a sweeping course, whether it be used directly upon the 

 glass table of the holder, or lifted from it by a very thin polished 

 steel washer. 



The dimensions are as follow : thickness ^ inch, width 2;^ inches, 

 length 3;^ inches. It is flat beneath, but is ground away above to a 

 thin edge on the cutting side, and on the upper surface is a removable 

 button for grinding. Below the centre of the ai'C of the cutting edge 

 is the excentric hole through which passes the pin that also per- 

 forates the glass table of the holder, and upon which it revolves. 

 When the blade is in place, a small washer and a short open spring 

 are to be slid on the pivot over it, and lastly a screw with a milled 

 head to make all tight. Now by withdrawing the knife to the left, 

 the lower edge just clears the margin of the ajierture for paraffin, 

 but as tlie blade descends to the right, its edge traverses the whole of 

 the aperture, with which its construction corresponds. 



With this arrangement it is easy to flood the object under 

 treatment. 



I have also used a very thin steel washer, 1^ inch radius, under the 

 blade, so that its cutting side can never be dulled by debris ujjon the 

 glass plate. 



The aperture of the cylinder in the holder is seven-eighths of 



