CHAPTER I. 9 



material, and vice versa. It may be well to possess the two sorts of 

 instrument ; but if only one can be afforded it should be such as will 

 give good work in either way. 



Microtomes fall further into two classes according as the knife 

 and the surface of section of the object are (A) in a horizontal plane, 

 or (B) in a vertical plane. The former offer greater facility for the 

 orientation of the plane of section, which is an important point for 

 the zoologist arid embryologist. Amongst these may be mentioned 

 (a) The " Sliding " Microtomes, in which the knife is carried on a 

 sledge and moved against the object (those of THOMA, SCHANZE, 

 REICHERT, and others). The THOMA, of medium size, as made by 

 R. Jung, Hebelstrasse, Heidelberg (No. 56 of his catalogue for 1911, 

 which may be obtained from Mr. C. Baker, 244, High Holborn, 

 London), is very suitable for the zoologist. It works equally well 

 with either paraffin or celloidin, and can be adapted as a freezing 

 microtome. But this (as is the case with the others above mentioned) 

 will not always furnish work of the highest accuracy ; for the knife 

 being only clamped at one end is liable to spring, and to give sections 

 of unequal thickness. This defect is remedied in (6), a type of 

 sliding microtomes in which the knife is clamped at both ends and 

 is a fixture, the object being carried on- a sledge and moved against it 

 (CAMBRIDGE SCIENTIFIC INSTRUMENT COMPANY'S large microtome, 

 the MINOT precision microtome, LEITZ'S, DE GROOT'S, JUNG'S 

 " Tetrander." This last seems to be near perfection ; see the 

 description by MAYER in Zeit. wiss. Mik., xxvii, 1910, p. 52 ; but is 

 more cumbrous than is desirable for ordinary work. 



Class A also includes some instruments in which the knife is 

 carried on a horizontal arm and swung against the object by a 

 rotary movement (JuNG, ROY, FROMME, REICHERT, THATE, and 

 others). I know nothing of these personally, but doubt their 

 constant accuracy. 



Class B contains some very fine instruments, admirably adapted 

 for the production of continuous ribbons of sections by the paraffin 

 method, but not so well adapted for celloidin or other work in the 

 wet way, or for soft objects. Amongst these are the New and Old 

 Rocking Microtome, made by TE SCIENTIFIC INSTRUMENT Co., 

 Cambridge, or by SWIFT & SON, or by JUNG, or by VAN DER STAD, 

 Amsterdam ; the MINOT, made by BAUSCH & LOME and the SPENCER 

 Model, or by BECKER (Gottingen), or by Zimmermann (21, Emilien- 

 strasse, Leipzig) ; the REINHOLD-GILTAY, made by J. W. GILT AY, 

 Delft. 

 For descriptions of the multitudinous models on the market see 



