88 CHAPTEE VII. 



This instrument is described jn Journ. Roy. Mic. Soc. (N.S.), vol. iii, 

 p. 2iJ8 ; the new Naples object-holder (which I consider 'essential for the 

 zoologist) is described and figured p. 915. See also the improvements 

 described op. cit., 1887, p. 334, and the latest price list of R. Jung (which 

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



W.C.). 



The BECKER microtome is also very much to be recommended (at least for 

 paraffin work : as to celloidin I cannot say). It is essentially on the same 

 principle as the Thoma, but possesses a mechanical arrangement for moving 

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

 nical arrangement, as in the Thoma model, but is put in motion by mecha- 

 nism. This is frequently an advantage. 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 mentioned are " all-round " microtomes; by which 

 is meant that they may be used either with a square-set knife or an obliquely- 

 set knife, and (Jung's at all events) 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 anything like the same infallible regularity, 

 certainly not with the same rapidity as the instruments next to be mentioned. 

 But they give excellent results, and in view of their adaptability to celloidin 

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

 ference, 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. 



All the instruments mentioned hitherto are sliding microtomes, that is 

 instruments in which the object to be cut is a fixture during cutting, and 

 the knife is moved on a slide and is only attached to its holder at one end. 

 This arrangement will not allow the highest possible accuracy to be obtained 

 with paraffin objects or any other hard objects. For with hard objects the 

 knife is free to yield slightly on meeting the object, instead of cutting its 

 way through it. This defect is fatal to the attainment of perfectly cut 

 series of sections of equal thickness throughout. For the highest class of 

 work it is necessary to employ a microtome constructed on the opposite 

 principle, namely one in which the knife is a fixture, and fixed at both ends 

 as near as possible to the cutting point ; the object being moved against it. 

 The following instruments are constructed on this principle, and for accurate 

 cutting of paraffin sections seem to me in general superior to any sliding 

 microtome. They also work incomparably quicker; and for this, and other 

 reasons, are better adapted than the sliding microtomes for cutting 

 continuous ribbons of sections. They cannot be considered to be " all- 

 round " instruments, because (although some of them are fitted with an 

 arrangement for that purpose) they a're not well adapted for giving to the 

 knife the oblique position and slow motion requisite for cutting objects of 

 very hard, or very soft, or very heterogeneous consistency. Also, the object 

 is placed in an awkward position for orientation and observation whilst 

 cutting. 



