ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1049 



which they have been preserved, and placed at once in a bath of melted 

 wax ; but the author thinks it is better to first dehydrate in absolute alcohol, 

 and then j^lace in a jireliminary bath of wax dissolved in chloroform. 

 Benzol and xylol will dissolve large quantities of the wax, but it is deposited 

 in a granular form on their evaporation ; but after solution in chloroform 

 the wax is left in a soli I form. Hence chloroform is preferred as a solvent 

 for the preparatory bath, but for all other purposes the less expensive 

 reagents may be used. The chloroform may be used over and over again, 

 and if occasionally a little fresh be added to it, the bath may be kept always 

 ready. 



The method of using myrtle wax is as follows : — The specimens are 

 dehydrated in absolute alcohol and then placed in a solution of wax in 

 chloroform as a preliminary bath, or transferred directly to the melted wax. 

 The pieces will be infiltrated in about the same time required by the paraffin 

 method. The pieces may be fastened on cork, by using the melted wax, or 

 imbedded in blocks of wax or jiaraffin to sujiport the specimen in the clamp 

 of the microtome. The sections are cut dry into benzol, washed in alcohol, 

 stained and mounted as usual. To completely remove the wax, it is best to 

 take the sections through a second bath of benzol, as any remaining wax 

 will be precipitated by the alcohol used in the washing. Warm absolute 

 alcohol may be used to free the sections from wax, but the benzol is better 

 and cheaper. Ordinary alcohol warmed will not dissolve the wax perfectly. 

 Warmed absolute alcohol will dissolve most of it, but will deposit it on 

 cooling. The author therefore thinks that the above method is preferable 

 to the immediate transferring from the preserving alcohol to the wax-bath, 

 as advised by Dr. Miller. The method is more rapid than the paraffin or 

 celloidin process; there is very little if any shrinkage; it does not injure 

 the most delicate tissues ; and it is inexpensive. If hardened in large masses 

 there is slight shrinkage and a tendency to crack ; this may be prevented 

 by the addition of a small amount of paraffin, with which it is miscible in 

 all proportions. The author states that he has never seen a section injured 

 by cracking. 



De Groot's Automatic Microtome.* — Herr J. G. de Groot's instrument 

 (fig. 248) consists of a rectangular frame, supported on four feet. To the 

 long sides of this frame are fitted two cylindrical bars, upon which the 

 object-carrier slides. The latter is a metal plate 6 faced with ebonite, and 

 supported on the slide rails by four feet : on its under side are two vertical 

 bars, joined at their ends by a cross-piece, from the centre of which uprises 

 a thick screw, and this latter passes through a threaded ring r. This screw- 

 ring supports two vertical bars, the upper ends of which pass through 

 openings in the metal plate and are then again united by a second ring. 

 To this last is fixed a third ring c, which supports a cup-shaped tube d 

 filled with paraffin for the reception of the object to be cut. At the lower 

 end of the main screw is a horizontal cog-wheel e by the movement of which 

 the ring r and with it the object-holder d are raised or lowered. The to- 

 and-fro movement of the object-carrier is effected by means of a rod which 

 connects with the large wheel/. The extent to which the screw is turned 

 in the to-and-fro movement is regulated by the escapement a. This is a 

 rod with rack which works up and down in a box and is fixed by a screw. 

 When the object-carrier moves backwards, the teeth of the rack grip those 

 of the toothed wheel c, so that the more they are engaged the deeper the rod 

 is pushed in. This depth is easily determined from the figures on the rod, 

 but it must be noticed that the hinder side of the box coincides with the 



* Zeitschr. f. Wiss. Mikr., iv. (1887) pp. H5-8 (1 fig.). 



