10 



(IHAPTHK I. 



to 



knife set square to the line of section. In the celloidin 

 method, as in the cutting of unimbedded tissues, it is 

 generally cut tcet, and always with the knife set d<niling. 

 Some microtomes that are well adapted for the paraffin 

 method are ill adapted for the celloidin method or the 

 cutting of unimbedded material, and vice vei-xa. It may be 

 well to possess the two sorts of instrument j but if only one 

 can be afforded it should be such as will give good work m 

 either way. 



Microtomes fall further into two classes according as 

 the knife and the surface of section of the object arc (a) 

 in a horizontal plane, or (b) in a vertical plane. The 

 former offer greater facility for the orientation of the j^lane 

 of section, which is an important point for the zoologist and 

 embryologist. Amongst these may be mentioned («) The 

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

 sledge and moved against the object (those of Thoma, 

 ScnANZE, Reichert, and others). The Thom.s of medium 

 size, as made by R. Jung, Hebelstrasse, Heidelberg (No. 56 

 of his catalogue for 1911, Avhich 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 microt(jme. But 

 this (as is the case with the others mentioned) will not 

 always furnish work of the highest accuracy ; for the knife 

 being only clamped atone end is liable to spring, and to give 

 sections of unequal thickness. This defect is i-emedied in 

 {h), 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 ScIE^■TI^IC 

 Instrument Company's large microtome, the Minot precision 

 microtome, Leitz's, de Gtrdot's, Jung's " Tetrander." This 

 last seems to be near perfection ; see the description by 

 Mayer in Zeit. viys. Mik., xxvii, 1910, p. 52 ; but is more 

 cumbrous than is desirable for ordinal'}' work. 



Class a also includes some instruments in which the knife 

 is carried on a horizontnl arm and swung against the object 

 by a rotary movement (Jung, Roy, Fkommk, Reichert, 

 Thate, a,nd others). I know nothing of these personally, but 

 doubt their constant accuracy. 



Chiss r. contains some very fine instruments, admirably 



