ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 735 



surface silvered. When it is desired to make a drawing, the object is 

 placed under one of the mirrors and the paper under the other. An 

 accurate outline is easily traced, and the drawing will be the natural 

 size of the object as long as both object and paper are on the same 

 horizontal plane. Modulating glasses for equalising the illumination 

 of the two sides are supplied with the apparatus. 



Modified Sedimentation Method for Demonstrating the Presence 

 of Bacteria.* — Dr. E. Strasburger recommends the addition of two parts 

 alcohol to one part fluid (urine, faeces diluted with water, &c.) when 

 contrifuging for bacteria. This addition lowers the specific gravity of 

 the fluid and facilitates the deposit of bacteria. The device is stated to 

 be specially adapted for tubercle bacilli in stools. 



New System of Obtaining Directing Marks on Microscopical 

 Sections for Reconstruction by Wax-plate Modelling.! — In the method 

 described by Prof. J. T. Wilson, the lines of direction are constituted 

 by actual definite strands of organised material imbedded in the sub- 

 stance of the paraffin block itself and in the closest and most intimate re- 

 lation to the object to be reconstructed. The materials used are the root- 

 bundles of the human Cauda equina. These, kept straight by means of 

 a weight, are stained with osmic acid and imbedded in paraffin. For 

 the imbedding a glass base-plate and a pair of imbedding bars are 

 needed. The glass plate should not be more than 2 or 3 mm. thick, and 

 on the centre part of its upper surface should be drawn or engraved a 

 square with sides measuring 2 cm. The outline should be blackened. 

 On the under surface of the plate deeply engraved lines are ruled 

 parallel to two of the sides of the quadrilateral. It is convenient to have 

 these lines at alternating intervals of 1 and 2 mm. The imbedding 

 bars must be rectangular throughout, with plane surfaces, and the length 

 of the arms should correspond to the dimensions of the quadrilateral 

 engraved on the base-plate. 



Two pieces of sufficient length are placed parallel to each other on 

 the glass plate and fixed thereto by means of heat. Over these the im- 

 bedding chamber is made. The object, oriented in the usual way, is 

 now in immediate apposition with the two black parallel lines, and these 

 lines have a definite relation to the sides of the paraffin block and to the 

 object. The steps of the process are detailed with great care and 

 minuteness ; but for these the original should be consulted. 



Biochemical Arsenic Reaction.J — Herr G. Marpmann describes at 

 some length and with approval the biochemical test for arsenic. This 

 test is well adapted for detecting arsenic in small quantities, e.g. hun- 

 dredth part of a milligram, and in organic solutions. The most con- 

 venient method is to inoculate sterilised bread-pap with a pure culture of 

 Penicillium, and moisten with the suspected fluid. A garlicky odour 

 arises in from 24 to 48 hours if arsenic be present. Selenium, tellurium, 

 and phosphorus give off characteristic odours with some resemblance to 

 garlic, but with a little practice and a normal nose the peculiar arsenic 



* Miinchener med. Wochenschr., 1900, No. 16. See Bot. Centralbl., lxxxiii 

 (1900) p. 237. t Zeitschr. f. wiss. Mikr., xvii. (1900) pp. 169-77. 



t Zeitschr. f. angew. Mikr., vi. (1900) pp. 143-53 (1 tig.). Qf. this Journal, 1899 

 p. 239. 



3 D 2 



