ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
685 
acid, and chrom-osmic acid, as hardening reagents. Picro-acetic acid 
followed by borax-carmine was the principal method. The staining 
process was aided by the heat of an incubator, and decoloration was 
effected by alcohol acidulated with hydrochloric acid. The preparation 
was mounted in glycerin or in clove-oil. Clove-oil is preferable to 
balsam, as it reveals more clearly the fibrous structure of the spindle, 
and allows of turning and pressing of the object at any time. 
Clove-oil causes the cytoplasm to become brittle, so that the body of 
the infusorian may be broken up by pressure or blows on the cover-glass, 
and thus the nuclear spindles be set completely free. In this isolated 
condition they can be studied to the best advantage, as they are not 
obscured by overlying cytoplasm. For the study of the chromatic 
figures clove-oil is too strong a clarifying medium. Glycerin or water 
will serve better. Hertwig examined the preparation first in clove-oil, 
then isolated the nuclear figures, washed in alcohol, and mounted in 
glycerin. He was thus able to study all parts and figures under most 
favourable conditions. 
Method of Narcotizing Hydroids, Actiniae, &c.* — Mr. H. B. Ward 
writes: — k£ In order to kill Hydroids, Actiniae, and similar forms in an 
expanded condition, a little expedient may be recommended which the 
writer has tried in many places and on many forms, and has uniformly 
found of value. The animals to be killed are left in a small quantity of 
the salt water in which they were brought in, until this becomes rather 
warm and stale, or until, in fact, they are weakened by the narcotizing 
effect of impure water. This manifests itself in one or two ways ; some 
forms draw themselves completely together, while others hang half 
expanded and limp in the water. They are then transferred in colonies 
or in large groups into [a] fresh [quantity of] salt water, which is at the 
same time cool. The eflect of a mass of cool, pure water is such as to 
cause the animals to expand fully and promptly. Immediately as the 
expansion is seen to reach its maximum, in the course usually of a few 
seconds, they are transferred by a quick motion into some rapid-killing 
reagent. After the long narcosis in poor water the polyps appear to lack 
energy to contract forcibly, as is usually the case. As killing reagents, 
alcoholic corrosive sublimate and picro-nitric acid have given the most 
uniformly good results. In this "way the most susceptible Actiniae may 
be easily preserved expanded and intact, and hydroids of all genera 
yield good specimens. The transfer to fresh sea-water is the only point 
requiring care. No time limit can be given, as the factors are too 
variable, but a little practice is sure to show the character and advan- 
tages of the method.” 
Method for Demonstrating the Formation of Acids by Micro- 
organisms.]* — Herr M. W. Beyerinck describes a method for showing 
the acidity or alkalinity of the products of micro-organisms. 
It consists in mixing a suitable medium, and one which will set well 
with very fine whiting, and then pouring the mixture into a glass 
capsule. The nutrient layer thus made is opaque and milky white. As 
coagulation media, gelatin, agar, or silicate may be employed. To 
* Amer. Nat., xxv. (1891) pp. 398-9. 
t Centralbl. f. Bakteriol. u. Parasitenk., ix. (1891) pp. 781-6 (1 fig.). 
