ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
485 
bouillon. This mass filters well through a hot-water filter, it is only 
liquefied over 30° C., and makes excellent plates which set in half an 
hour without the aid of ice. 
The addition of the small amount of agar does not prevent the 
liquefaction of the medium by peptonising bacteria, though the action is 
less rapid than on gelatin alone. 
The gelatin may be clarified in the usual way by means of egg 
albumen or by means of “ clearing clay,” a magnesium-aluminium 
hydrosilicate, which in conjunction with water is decomposed into the 
hydrate ; and this in the nascent condition has the property of throwing 
down all muddy and even colouring matters, leaving a clear and colourless 
supernatant fluid. When the gelatin or agar solutions are ready for 
filtering, 1 per cent, of clearing clay is added, and having been well 
shaken the mixture is steamed for one hour before it is filtered. 
Production of Plague Serum.* — Herr G. Gabritschewsky, finding 
that living cultures of plague bacillus were unsuitable for immunising 
horses, made experiments for the purpose of obtaining immunising and 
toxic substances from cultures of Bacillus pestis by plasmolysis. In 
bouillon with 4 per cent, glycerin the plague bacillus grows freely, on 
pure glycerin at 37° not at all. Horses were immunised by means of 
cultures sterilised by the addition of glycerin. Agar plates were inocu- 
lated from bouillon cultures, and in 24-48 hours at 37° a copious plague 
culture was obtained. This was distributed in test-tubes, each containing 
2 ccm. of glycerin. In 24 hours a cloudy slimy mass was formed, and 
this diluted with an equal bulk of bouillon was injected subcutaneously 
into horses. At the injection site considerable infiltration occurred, and 
the temperature rose to 39*2°. On intravenous injection the tempera- 
ture rose to 40°, falling again after 24-48 hours. This immunising 
method is only suitable for horses, as glycerin by itself is poisonous 
to mice, and in rabbits and guinea-pigs causes local necrosis. 
The rest of the paper is devoted to the plasmolytic method of 
sterilising cultures. 
Culture of Pleurococcus.f — Miss Dorothea F. M. Pertz recommends 
for the culture of this organism Knop’s solution 0 * 2 per cent, in sterilised 
glass dishes and flasks ; also in hanging drops of the same solution. 
Chodat’s filamentous form of the alga did not occur. 
(2) Preparing- Objects. 
Method for Preparing Plankton Organisms. :£ — Herr G. Marpmann 
gives the following for preparing soft organisms such as plasmodes, 
Radiolaria, Infusoria, &c. A 1 per cent, solution of hydrochlorate of 
cocain is added to the fluid to be examined in the proportion of one- 
third to one-half the volume of the latter. Observation under the 
Microscope shows that the organisms, even the lower plants, lie quite 
still, their processes, tentacles, &c. being fully extended. A drop of 
formalin is then added. This kills and fixes the organisms at once. 
* Russ. Arch. f. Pathol., klin. Med. u. Bakt., 1897. See Centralbl. Bakt. u. Par., 
l te Abt., xxiii. (1898) pp. 808-9. 
f Rep. Brit. Ass. Toronto, 1897 (1898) p. 864. 
t Zeitschr. f. angew. Mikr., iv. (1898) pp. 42-3. 
