Microscopy. 1141 
porate out the requirements to be fulfilled by such reagents, lays 
own the principles by which one should be guided in selecting 
them, and concludes by giving a method which has proved to be 
eminently satisfactory. 
Rules.—(a) For fixing tissues it is important to use reagents that 
do not form tissue-like precipitates with protoplasm. This require- 
ment is met by chromic salts, sulphate of copper, sublimate and some 
other salts. Preparations in chromic salts, when transferred to alco- 
hol, should be kept in absolute darkness (H. Virchow), until the fix- 
ing reagent is removed so far as possible. 
(b) All reagents which transform protoplasm into tissue-like 
forms, as, e.g., chromic acid, should be avoided, or their application 
must be controlled. 
(c) Fixing fluids should contain an organic acid, e.g., acetic acid, 
which changes nuclein into an insoluble state. The acid must be 
used in a diluted form, as nuclein is dissolved in strong acids. 
The time of action must be short, as the long-continued action of 
even a weak acid dissolves nuclein. 
(d) It is desirable that the fixing fluid should contain alcohol in 
a small quantity. 
- Strong alcohol dehydrates and induces changes in the protoplasm. 
Kultschitzky’s Fluid.— Add, ad libitum, pulverized bichromate of 
potassium and sulphate of copper to alcohol (50 per cent.). Keep 
in absolute darkness twenty-four hours. A transparent greenish- 
yellow fluid is thus obtained, which is to be acidulated before use 
with acetic acid (5 to 6 drops to 100 ce.). 
Method.— Place the object in the fixing fluid for from twelve to 
twenty-four hours, according to its size and hardness, and keep in 
the dark ; then transfer to strong alcohol. After twelve to twenty- 
four hours the preparation is hard enough for cutting. 
Conservation. =Kultechiteky thinks that for conservation only 
such fluids should be used as produce no further changes in proto- 
plasm after it has once been fixed. As alcohol, Miiller’s Fluid and 
other fluids in common use do work changes in the tissues, 
ee pernliaky recommends keeping preparations in ether, xylol, or 
Accessory Nuclei (Nebenkerne, Paranuclei).—Dr. Gustav Platner 
has been for some years en with the problem of the origin 
and meaning of accessory nuclei in gland-cells. The results of his 
work have not yet been published, so far as I am aware; but some — 
of his methods of study have been given in the Zeitschrift fiir wis- 
ifiliche Mikroskopie, Vol. IV., No. 3, p. 349. Flemming’s 
chrom-osmio-acetic acid is the best hardening, or “ fixing” medium. 
This mixture may sometimes be modified to advantage by dimin- 
ishing the quantity of acetic acid and increasing that of osmice acid. 
en the accessory nucleus forms a compact mass, as In reptiles 
