A New Freezing Microtome. 189 



the further addition of the freezing mixture, or by dropping water 

 or a three-quarter per cent, salt solution at the ordinary temperature 

 on the surface of the frozen tissue, or by heating the razor slightly. 

 With regard to the process of section, it may be stated that a razor 

 answers perfectly well for all ordinary purposes. The blade should 

 always be JioIIow on both surfaces (E, Fig. 2). It is a mistake to 

 employ a flat knife, for it is scarcely possible to keep the surface of 

 the brass table of the machine smooth enough to permit of the knife 

 lying quite flat. The knife should be imslied obliquely through the 

 tissue, which should be cut at one sweep. This is not possible with 

 a frozen tissue if the ice be too hird. For an unfrozen tissue 

 imbedded in the parafiin the knife should be wetted with methylated 

 spirit. This is dropped upon the knife from a funnel with an elastic 

 tube depending from it, clamped by a Mohr's clip. The funnel is 

 suspended at a convenient height above the machine. The spirit 

 keeps the blade perfectly clean, and it forms a pool upon it, which 

 enables the section to float over the surface with ease. In the case 

 of freezing it is not necessary to wet the knife, for the melting ice 

 readily does so. 



Mr. McCarthy has modified my original machine by causing 

 the ice box to project at the right as well as at the left side of the 

 brass table (or the knife). I cannot at all approve of this modifica- 

 tion, because it interferes very seriously with the movements of the 

 right hand in the process of section. I have studiously avoided 

 such an arrangement from the very first. The points in which my 

 new differs from my old machine are these. The table for the 

 knife (B) and the freezing box are larger. The escape tube (H) is 

 larger, and the indicator is constructed upon a better principle. I 

 advise those who may have obtained my old machine from Hawksley 

 to get the freezing box made twice as large, and they will find it a 

 very serviceable instrument, although, owing to the coarseness of 

 the screw, necessitated by the nature of the indicator, that machine 

 cannot give such a reliable result as that here described. The 

 pathologist, the physiologist, the zoologist, and the botanist will 

 find this machine of the greatest service. It supplies a desideratum 

 long needed. But I must refer them to my forthcoming work on 

 *' Practical Histology' for the special indication of the cases in which 

 it is most applicable. In conclusion, I would express my gratifica- 

 tion that so skilled a microscopist as Mr. Needham has publicly 

 testified * to the advantages which my method of freezing tissues 

 for the purposes of microscopy possesses over all others that have 

 been hitherto proposed. 



The new microtome is made by Baker, of High Holborn. — The 

 Lancet. 



* ' Monthly Microscopical Joiirnal,' June, 1873. 



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