ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 383 
eosinophile granules are entirely uncoloured and unchanged. Amplio- 
phile granules are stained blue, while the basophile granules appear 
violet with daylight, and brilliant rose with yellow light. The substance 
which produces the rose-coloured modification of methylen-blue does so 
whether it be present as granules in the cell-substance, or dissolved in 
the surrounding fluid. The study of the living cells and their behaviour 
towards noxious or innocuous substances has been carried out by injecting 
various substances into the lymph-spaces of the frog, and withdrawing 
drops of lymph for examination at varying intervals of time, and by 
hanging drops. The hanging drops were suspended on the under side of 
a cover-slip in moist chambers, sufficiently large to provide air enough 
for the needs of a small drop of lymph for about ten hours, without 
introducing a fresh supply. The cover-slips used were always carefully 
cleaned with acid and absolute alcohol, and then sterilised by heat, 
immediately before use. 
Gold Impregnation.* — Mr. C. L. Bristol gives an account of a method 
of using formic acid and gold chloride suggested to him by Miss J. B. 
Platt. He has used it in tracing the nervous system of Nejphelis lateralis , 
and has found it reliable. In leech tissues it differentiates all nerve 
tissue, though the results with other tissues are poor. It has been 
used successfully on larval vertebrate material also, by varying the 
strength of the formic acid, or the time of its application. The follow- 
ing process was employed : — The leech is put into 20 or 30 times its 
bulk of 10 per cent, formic acid, and left from 3 to 5 minutes. It dies 
well extended. It must now be transferred without washing to 1 per 
cent, gold chloride for 25 minutes, then put without washing into 1 per 
cent, formic acid for 24 hours, or until reduction is complete. This is 
indicated by a rich purple colour over the whole specimen. It must 
now be washed slightly in tap water ; run up through the alcohols to 
chloroform, saturated with hard paraffin. When the impregnation 
appears to be very slight, stain the sections on the slide with erythrosin 
or some other deep red anilin stain for contrast. These sections will 
often show the most exquisite details. Transparent larvae 5 to 10 mm. 
long require a milder treatment, such as 5 per cent, formic acid for 2 or 
3 minutes, 1 or 4 per cent, gold chloride for 10 minutes, weak formic 
acid for 1 to 4 hours. The reduction of the gold chloride may be 
stopped at any point by transferring to alcohol. The gold chloride 
solution was exposed to sunlight for some time before using ; this may 
not be an essential factor in the process, but it has been suggested that 
failure to ripen the solution by sunning may be the cause of many of the 
failures in gold staining. 
Brain of Pike.j" — Herr L. Neumayer used the chrom-osmic-silver 
method as modified by Ramon y Cajal. The objects were placed in a 
mixture of 1 part of 1 per cent, osmic acid and 4 parts of 2 per cent, 
potassium bichromate solution. He left the objects two days in the 
osmic acid and potassium bichromate solution, two days in 0*75 nitrate 
solution. To add a few drops of formic acid to the silver nitrate solu- 
tion is very advantageous. A second or third repetition of the whole 
* Amer. Natural., xxviii. (1894) pp. 825-6. 
f Arch. f. Mikr. Anat., xliv. (1895) pp. 345-65 (1 pi). 
