ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 165 



1-058 as comparer! to water, the true number would be 4937 X 1*058 

 = 4667-3 in one gram, or 4667 ■ 300 in a kilogram, or 4667 ■ 3 X 453 • 593 

 = 2,117,054 in one pound avoirdupois. 



Models in Metal of Microscopical Preparations.* — Prof. E. Selenka 

 prepares metal models from microscopical preparations in the following 

 way : — To obtain a plaster representation of tbe brain of a vertebrate 

 embryo, tbe outlines of tbe bead, tbe external and internal boundary 

 lines of tbe brain are drawn on paper from tbe specimen witb a camera 

 lucida. According to tbe size of tbe separate sections, every second, 

 tbird, or fourth section is selected, the drawings are numbered, and then 

 carefully stuck on cardboard of the necessary thickness ; the reverse 

 side of the cardboard is covered with glue. The separate figures are 

 then carefully cut out. Small strips for joining must of course be left 

 in the brain. The different layers of cardboard are then glued together in 

 their proper order, and thus a case model of the head is obtained. Any 

 gaps or seams on the surface are filled in with plaster of Paris, and 

 then tbe hollow model, which is open behind, is filled with Wood's metal 

 heated to about 75° 0. When cool the cardboard is softened in lukewarm 

 water and then stripped off. The model is next cut in two with a fret- 

 saw and the internal surface of the brain freed from the cardboard. 

 Unevenness of the surface and holes are easily got rid of with a heated 

 needle or knife, or by touching up with a stick of Wood's metal which 

 has been softened at a gas jet. It is necessary to leave vent-holes in the 

 cardboard model. 



New Reagent for Albuminoids.! — Dr. M. Kronfeld proposes a new 

 test for the presence of albuminous substances, viz. alloxan (= mesoxa- 

 lylurea). This substance forms crystals which are readily soluble either 

 in water or alcohol. From a hot solution there are deposited small 

 permanent crystals with 1 equivalent of water ; the larger crystals which 

 are obtained from a warm solution deliquesce in the air. Solutions of 

 alloxan produce, with albuminoids, and with some of tbe products of its 

 decomposition, a red colour, which passes into purple, with an unpleasant 

 odour. The reaction is obtained with tyrosin, very intense with aspara- 

 ginic acid and with asparagin ; apparently with all those compounds 

 which contain in their molecules the group CH 2 . CH(NHo) . C0 2 H. 



Solutions of albuminoids give the reaction more slowly than when in 

 the solid form. In order to be certain of success it is necessary to 

 operate in the cold, and to exclude as much as possible the presence of 

 ammonia ; solutions in alcohol, water, or in caustic soda may be used. 

 Free acids prevent the reaction. The endosperm of seeds, which contains 

 aleurone and sphseroerystals, is very convenient for experimenting with 

 the alloxan-reaction. 



White's Elementary Microscopical Manipulation.^ — Whilst it 

 might be thought that the ground was already fully occupied for works 

 on microscopical manipulation, Mr. T. Charters White's excellent little 

 book will be found to meet a distinct want. More extensive treatises of 

 course exist, but this, in the words of the author, " is designed with the 

 aim of affording the youngest beginner such directions for preparing 



* SB. Fhysiol. Med. Soc. Erlangen, 1886, Heft 18. 

 t SB. K. Akad. Wiss. Wien, xciv. (1887) p. 135. 



i White, T. O., ' A Manual of Elementary Microscopical Manipulation for the 

 use of Amateurs,' iii. and 104 pp., 1 pi. and 6 figs. Svo, London, 1887. 



