ZOOLOGY AND BOTANY, MICROSCOPY, ETC. (371 



way that its epithelial surface is turned upwards. During this operation 

 desiccation of the tissues is avoided by sprinkling them with aqueous 

 humour, blood-scrum, or cliloride of sodium in 7/1000 solution; the 

 membrane is maintained in a state of extension by a ring of platinum 

 which is fixed on the disc of the moist chamber ; the ring must be of a 

 little longer diameter than that of the disc, in order that the membrane 

 may be held between it and the disc. The membrane is covered by a 

 glass plate, which is fixed with parafiin. In such a preparation the cells 

 with vibratile cilia, sensory or glandular cells, striated muscular fibres, and 

 nerve-fibres and cells may be easily observed in the living state. As the 

 ring keeps the membrane in its place, the glass cover may be removed for 

 the purpose of adding reagents. 



Investigating- the Termination of Nerves in the Liver.* — Mr. A. B. 

 Macallum adopted the following method for demonstrating nerve-structures 

 in the liver of Neduriis ( = Mcnobranchus). Pieces of the liver were 

 hardened for a week or more in Erlicki's fluid, or for several days in a 

 1/6-1/5 per cent, solution of chromic acid. After the hardening was 

 sufficiently completed in alcohol, sections of the frozen tissue were made 

 with a Cathcart microtome. When the gum was carefully removed these 

 were put in a 5 per cent, solution of formic acid for an hour, transferred to 

 a 1 per cent, solution of gold chloride for about twenty minutes, then 

 washed in distilled water, and the gold afterwards reduced in the dark with 

 a 10 per cent, solution of formic acid. About thirty hours suffices for this 

 reduction at a temperature of 20^ C, and the sections then have a deeji red 

 colour, though the tinge was sometimes violet. The chromatin of the 

 nuclei of the hepatic cells took a deep blue-violet tint, the caryoplasm light 

 violet, while the cytoplasm came out very distinctly as a meshwork with a 

 pink or light carmine colour ; the nerve-fibres appeared deep violet, but the 

 connective tissue of the interlobular spaces attained a light, or sometimes a 

 deep red colour. When chromic acid was used as a hardening reagent the 

 addition of any organic acid at the same time, such as acetic acid more 

 especially, seemed to have the effect of robbing the nerve-fibres of their 

 selective capacity for gold. Sections of the liver of Necturus are of no 

 value when they are less than • 02 " m " [mm.] in thickness. With the 

 human liver preparations proved to vary very considerably, but were often 

 not successful. 



All the sections were cleared in oil of cloves and mounted in balsam. 

 The study of the ultimate terminations of the nerves was made with the 

 Leitz 1/12 in. homogeneous immersion, with special illumination. 



The author discusses the value of gold chloride as a reagent for 

 differentiating nerves, which is not admitted by all histologists; he 

 thinks that it has many advantages over other reagents; the substance 

 which fixes the gold in a violet form is not confined to nerves, but appears 

 to be diffused to a small degree in other tissue elements ; the failures of 

 some histologists are referred to their not having sufficiently hardened the 

 tissues. Osmic acid, although useful in the case of medullated nerve- 

 fibres, is of no value for demonstrating the finest non-medullated fibrils. 



Preparing the Amphibian Egg.j — Prof. 0. Schultze has found that 

 for hardening-fluids the following mixtures give perfectly satisfactory pre- 

 parations when used in the manner described below : — (1) Chromo-osmio- 

 acetic Acid: Chromic acid (1 per cent.) 25 parts; osmic acid (1 per cent.) 



* Quart. Journ. Micr. Sci., xxvii. (1887) pp. 443-8. 



t Zeitschr. f. Wiss. Zool., xlv. (1887) p. 185. Cf. Amer. Naturalist, xxii. (1S87) 

 pp. 595-6. 



