ZOOLOGY AND BOTANY, MICKOSCOPY, ETC. 771 



2, 4, 6, &c, up to 20 gmis. by weight of celloidin. The dehydrated 

 tissue is placed successively in the ten bottles for 24 hours. If it is to 

 be cut immediately, the tissue is mounted on a block and hardened in 

 chloroform for 15 to 20 minutes, or in 80 p.c. alcohol for several hours. 

 If it is to be kept for some time, the piece is removed from the 20 p.c. 

 solution with a thick layer of celloidin surrounding it and dropped into 

 chloroform to harden it, after which it is kept in a solution composed 

 of equal parts of 95 p.c. of alcohol and glycerin. When wanted for 

 cutting, the tissue is wiped dry with a clean cloth, a thin layer of 

 celloidin is shaved off, and the piece immersed in 6 p.c. celloidin for 

 several minutes ; then mounted on a block and hardened in chloroform. 

 The only inconvenience attached to this method is that it takes 12 days 

 at least, but its many advantages amply compensate for the extra time 

 .and trouble. 



Use of Paraffin Imbedding- for Medullary Sheath Staining.* 

 G. L. Streeter bases the method he advocates on the supposition that 

 the failure of Weigert's method with paraffin sections is due to the solvent 

 action of xylol on the myelin during the process of imbedding. He 

 stains the tissue in bulk witli Weigert's hematoxylin, after it has 

 been passed through Miiller, or some other chromic solution, and 80 p.c. 

 alcohol. He then brings it into paraffin, melting at 50° C, through 

 70 p.c. alcohol, absolute alcohol and xylol. Sections are cut and fixed 

 -on the slide in the usual way, and brought into water through xyol and 

 alcohol. They are then ready for differentiation, which can be accom- 

 plished either by Weigert's solution of potassium ferricyanide and borax, 

 which the author uses diluted ten times, or by the modification of Pal. 



New Method for the Preparation of Horizontal Sections of Thin 

 Laminated Vegetable Flat Tissues. — P. F. Reinsch f recommends the 

 following method. The substance is first macerated either in water or 

 in some caustic solution, e.g. KOH or H 2 S0 4 . After this it is washed, 

 .and lifted oiit on a glass plate. If a caustic solution has been used 

 this is first neutralised with NH 3 or HC1. During the maceration 

 a good deal of gum is probably developed, and by this the substance, as it 

 dries, sticks of itself to the glass plate. If not, then gum or a trans- 

 parent alcoholic solution of resin must be used, care being taken to 

 avoid flatness and the inclusion of air bubbles. The next step is 

 the separation of horizontal layers as desired, and this is accomplished 

 by carefully damping the flat surface of the object firmly adhering to the 

 glass plate, not its edges, and separating the topmost layer by means of a 

 special microscopic scalpel, which the author makes himself in three 

 shapes out of ordinary medium-sized needles, grinding the half towards 

 the eye end to form a cutting edge, and mounting on holders. He uses 

 .this method for such delicate objects as flower petals. 



Mi not, C. S. — History of the Microtome. Parts I. and II. 



Journ. App. Mier., VI. (1903) pp. 2157-60, 3 figs., pp. 222G-8, 1 fig. 



* Arch. Mikr. Anat, lxii. (1903) pp. 734-9. 

 f Zeitschr. Wiss. Mikr., xx. (1903) pp. 28-33. 



