ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
815 
to be still perfectly level — and bring the bubble of the spirit-level to its 
central position by turning the screws b. We have thus brought the 
crystal into the required position for grinding the face C, which, laying 
the levelling tripod aside, we proceed to do. 
The adjustment of the face A in the zone of the faces f F f" is made 
on a reflecting goniometer with a horizontal limbus, such as that of 
Websky-Fuess No. II. or III. A ring T (fig. 95) serves to hold the 
cylinder on the goniometer. Instead of depending upon calculation, the 
correction in the position of the crystal can be often sufficiently accu- 
rately made by two or three trials, a small surface being ground and 
polished, and its accuracy being tested on the goniometer without 
detaching the crystal from the brass cone or the latter from the 
cylinder.* 
Obregia, Al. — S erienschnitte mit Photoxylin Oder Cello'idin. (Serial sections 
with photoxylin or celloidin.) Neurol. Centralbl ., 1890, No. 10, 3 pp. 
Ross, J. F. W. — Paraffin Method as used by Prof. Gaule, Zurich. 
Canxd. Pract., XIV. (1889) p. 409. 
(4) Staining- and Injecting-. 
Staining with Chloride of Gold.j — Prof. A. S. Underwood writes : — 
“ I have long regarded this agent as one of the most useful for the 
observation of the dental tissues. I know of no other stain which so 
clearly marks out the minute anatomy of the soft tissues which pene- 
trate bone and dentine ; in fact, its excellence as a selective stain would 
long ago have obtained for it a much more widespread popularity were 
it not for the fact that it has been generally regarded as specially liable 
to failure in manipulation. Almost all the recognized text-books speak 
of it as a very difficult stain to employ successfully, and as requiring a 
very lengthy and troublesome method of procedure, and as only appli- 
cable to perfectly fresh tissues. I have found, after some eight years of 
pretty constant use, that the subjoined method is easy to employ, does 
not take long, and is, moreover, both certain and fairly permanent in its 
results. 
First, about the tissues to be stained. They do not require to be 
very recently dead ; the fresher they are the more quickly they take the 
stain, but I have stained scores of sections of teeth and bone that had 
been severed from the living body for a long time, sometimes for weeks. 
It is better to avoid as far as possible the use of metal instruments, 
bone, wood, or quill being preferable ; the use of steel does not, however, 
doom the staining to failure. The method I adopt is as follows : — 
(a) Wash the sections in solution of bicarbonate of soda. 
(b) Put some 1 per cent, solution of chloride of gold in a watch-glass, 
test it with litmus-paper, and if it be acid add bicarbonate of soda by 
drops till it is neutral ; place the sections in the solution and cover the 
watch-glass with some lid to keep it in the dark (the lid of a china pot 
such as is used for potted meat serves very well) for from half an hour 
to an hour, until the sections look straw-coloured. 
(c) Remove sections from staining fluid to distilled water, and leave 
* We understand that this instrument is only to be obtained from Herr Zimmer- 
mann, Hauptstrasse, Heidelberg. 
f Journ. Brit. Dental Assoc., xi. (1890) pp. 696-7. 
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