A WORD ON MICROTOMES. 167 



the first place in order of date belongs to the THOMA sliding 

 microtome. This is made in several sizes by H. Jung, 

 Mechaniker in Heidelberg. For zoological and general histo- 

 logical work I recommend the medium size (No. 2a or 4), with 

 the newest Naples object-holder and newest form of knife and 

 knife-holder. 



This instrument is described in Journ.Roy. Mic. Soc. (N.S.), 

 vol. iii, p. 298 ; the new Naples object-holder (which I consider 

 essential for the zoologist) is described and figured p. 915. 



The BECKER microtome is in many respects an improvement 

 on the Thoma model. It is essentially on the same principle, 

 but possesses a mechanical arrangement for moving the knife- 

 carrier; that is, the knife-carrier is not only guided by a 

 mechanical arrangement, as in the Thoma model, but is put 

 in motion by mechanism. This, I think, is certainly an 

 advantage. Another improvement is that the slides are made 

 of glass instead of metal; this allows one to dispense with 

 the use of oil to the slides, which in the Thoma model gives 

 rise to inequality in the thickness of sections. A minor point 

 is that the instrument is somewhat cheaper than the Thoma 

 form. It is made by Aug. Becker, Gottingen. Descriptions 

 of two forms (Spengel and Schiefferdecker) will be found in 

 Journ. Roy. Mic. Soc., 1886, pp. 884 and 1084. The Naples 

 object-holder can be fitted to the Becker microtome. 



The instruments above described are " all-round " micro- 

 tomes ; by which is meant that they may be used either with 

 a square-set knife or an obliquely-set knife, and will cut 

 either celloidin sections or frozen preparations (if a freezing 

 apparatus be added to them) just as well as paraffin sections. 

 They will not, according to my experience, cut series of 

 paraffin sections with quite the same infallible regularity, 

 certainly not with the same rapidity as the instruments next 

 to be mentioned. But they give results of almost the highest 

 attainable quality, and in view of their adaptability to celloidin 

 or other semi-soft preparations, I think that one of them, the 

 Becker by preference, should be the instrument chosen by the 

 worker who desires not to be entirely confined to the paraffin 

 method, and who cannot conveniently possess more than one 

 microtome. 



The beautiful Cambridge rocking microtome (furnished by 

 the Cambridge Scientific Instrument Company, St. Tibb's 



