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October 16th, 1885. 

 F. W. BRANSON, F.C.S., on "MICROTOMES." 



The word " microtome " is not to be found in most dictionaries ; it is 

 not, therefore, popularly understood. Like very many other scientific 

 terms of recent origin, it is derived from the Greek. The first root in the 

 word (mikros — small) goes to form the tirst part of several names of 

 scientific instruments, as microscope, microphone, &c., and of scientific 

 terms, as micrograph, microcosm, &c. ; and the other part of the word {tome 

 — section or cutting) is from the Greek root tomos. There is also a well- 

 known Latin word, tome, which means a section, or part of an author's 

 work, and which we freely render as a " volume," that is derived from the 

 same Greek root. It is obvious from this that the object of a microtome 

 is to produce small sections or slices of various substances. These sections 

 are intended to be submitted to microscopical examination, and it is 

 therefore indispensable that they should be verj-^ thin, and of equal thick- 

 ness throughout. How thin they should be (within certain ranges) depends 

 on what particular substance it is desired to examine, but the microtome 

 is not uncommonly required to pi'oduce slices of no greater thickness than 

 the five-thousandth part of an inch ; or to put this in a practical way, 

 supposing it is desired to examine throughout, in a transverse plane, the 

 head of a blue-bottle fly, whose head has a longitudinal diameter of, say, 

 one-eighth of an inch, then this head must furnish six hundred and twenty- 

 five slices (625) ! This illustration may furnish a key, roughly speaking, 

 to the extreme interest attaching to machines that are required to produce 

 such delicate results. 



Some substances may be sliced by the microtome without previous 

 preparation ; but others, as animal substances in a mass, require to be 

 frozen ; and other substances, whether animal or vegetable, of a fragile 

 character, need to be first hardened and then embedded in some matrix 

 which will hold them in a true position, and, at the same time, relieve the 

 cells from the crushing efi'ect of the action of cutting. The microtomes 

 of Weigert, and of Rivet, exhibited among others, are capable of 

 adaptation to make sections under all three of these circumstances 

 mentioned — i.e., without previous preparation of the object, by freezing 

 the object, or by imbedding the object in a foreign substance. Then the 

 mode of freezing the object varies. By means of one of Williams's micro- 

 tomes the object is frozen by an ether spray; in another of his instruments 

 by a mixture of ice and salt. The ether spray is also employed for freezing 

 in the two first-named instruments. But one instrument, the " Cambridge 

 Rocking Microtome," absorbed a large share of attention. This instrument 

 is so called in allusion to the motion of the limb which holds the object, 

 imbedded in paraffin, and brings it down on the cutting edge of the razor ; 

 but the principal interest attaching to it arises from its producing the 

 sections in a serial or riband form, the great advantage arising from which 

 consists in its thus presenting the successive slices of the object in perfect 



