782 SEC. 18. BIOLOGY. 



3648. Microtome, with four moulds, water-trough, wedge- 

 shaped steel disc. Prof. R. Mobius, Kiel. 



3649. Two Microtomes, with three moulds and steel disc. 



Prof. R. Mobius, Kiel. 

 A written explanation accompanies the objects exhibited. 



3650. Five Moist Chambers, for microscopical research 

 (after the designs of Recklinghausen, Ludwig, Geissler, de Bary, 

 and Krebs). Geissler 8? Son, Berlin. 



3651. Fritsch's Sliding Microtome. 



Prof. G. Fritsch, Berlin. 



The microtome, of which (on account of some recent alterations) an 

 incomplete account is sent, has on its left a movable box for the reception of 

 the object, on the right a pusher (Schieber) with eccentric screw as a holder 

 for the knife. Other knives will be found in the lid for use, according to 

 the degree of resistance offered by the object. 



The object to be cut must be so placed in the metal box that the part to be 

 cut projects over the upper rim of the box. The preparation is imbedded in a 

 suitable mass, or is frozen in a mixture fit for cutting (e.g. Rutherford's). In 

 the brown lacquered box are plates of spermaceti, and mixtures of the latter 

 with cocoa-butter, suitably selected. Some elder pith is imbedded as a 

 specimen. 



After an advantageous position, as regards the object, has been given to 

 the knife, and the object has been fixed in its little box by means of the 

 screw of the large movable box, so that it can be cut by a gentle elevation of 

 the movable box, the screws of the disk and knife are sharply drawn across. 

 Should the position of the object be too low, one of the metal plates furnished 

 with the apparatus is laid under the box, and the screw of the movable box 

 again turned up, but not too quickly, in order to prevent the strain and pres- 

 sure on the side of the box becoming too great. The work of preparing is 

 automatic, so that when a clear section surface is obtained, the movable box, 

 by means of the vernier attached, can be raised a definite fraction in height, 

 and. the object fixed in this situation; the knife screwed up on the slides is 

 guided by means of the horizontal slot, whereby the uppermost part is taken 

 off as a thin se 2tion. After drawing back the knife to the other end of the 

 slot (turned from the operator), and a fresh raising of the box, a second 

 section is obtained in a similar manner, and .so on until the object is con- 

 verted into thin sections. With objects difficult to cut it is necessary to 

 moisten the blade during the cutting of the section with weak spirit contained 

 in a wash bottle, one tube from which overhangs the blade, whilst the other 

 is kept in the mouth for blowing. If the objects resist very much, so that 

 the blade tends to give, then the safety of the section will be secured by 

 laying the curved piece of metal from the mahogany box under the larger 

 screw of the eccentric disk, and a corresponding tightening of the adjusting 

 screw placed at the free end of the knife. The box for objects can (for the 

 purpose of keeping the left hand for guiding) be easily fixed by means of a 

 clamping screw through the slot. 



Some sample sections are contained in the mahogany box. 



3652. Counting Micrometer, for enumerating microscopical 

 forms. To this is added a figure under glass, representing the 

 micrometer magnified eight times. 



Prof. H. Wolcker, Halle an der Saale. 



