NEW FORM OF SECTION-CUTTING MACHINE. 277 



refuse alcohol, in wbicli a gum preparation has been hardened, after 

 which it acquires an oily consistency. 



When the material to be cut is so very delicate that any undue 

 pressure would destroy it, I make the cavity in the carrot much 

 larger than the material to be cut, and fill up the superfluous space 

 with bits of dry elder pith ; these are carefully packed in between 

 the carrot and the material, the movable side is then gently pressed, 

 not screwed down ; the pith is wetted with alcohol, which causes it 

 to swell evenly in every direction, adapting itself to all the parts 

 without unduly compressing them, and holding the material firmly, 

 while it gives a steadying influence to the edge of the knife, and 

 prevents it from slipping when an extremely thin section is being 

 cut, a mishap that often occurs with carrot. 



I use no other matrix than the two I have mentioned ; the latter 

 I found in use at the College de France, and it is extremely ser- 

 viceable. Of course anyone having a predilection for wax or 

 paraffin can use them .in a hole made in the -block of carrot, just 

 as they would use the tube apparatus for that purpose ; indeed, all 

 the advantages of that apparatus are to be found in my machine, 

 with all its own advantages superadded, none of which are pos- 

 sessed by the tube machine in any of its innumerable modifica- 

 tions. 



The method of determining the thickness of sections to be cut 

 is very simple. The feeding screw (b) has 25 threads to the inch, 

 consequently each turn of the screw moves the table forward 

 l-25th of an inch. A 12-toothed wheel, on side I, is fixed on the 

 end of the screw, and if this be turned round the distance of one 

 tooth or space, that is 1-1 2th of a turn, then the table moves for- 

 ward the l-12th part of the l-25th of an inch; or, in other words, 

 the l-300th of an inch, the thickness of such section if one was 

 cut. One half of a space would give 24 times 25, equal to 600, and 

 so on. 



I may remark also that the cavity of the machine now before you, 

 which is 1-|^ inch cube, is made of the most convenient size for 

 ordinary work ; it will possibly occur to some of you that it might 

 be made to cut much larger sections. This is quite true, though I do 

 not advise it ; but it is easy to enlarge it by the addition of three 

 extra pieces adapted to the present machine, which shall cut any re- 

 quisite size of section ; indeed, within the last three "weeks I have, 

 with the assistance of my wife (who is no mean microscopist), 



