824 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Silicate-jelly as a Nutrient Substratum.* — Herr P. Sleskin, who has 
used the substratum of silicic acid, relates his experience in following 
out the preparation of the silicic acid as directed by Kiihne, and its 
further modification according to Winogradsky, for cultivating nitrifying 
organisms. Three volumes of silicate of soda diluted to a specific gravity 
of 1-08 are mixed with 1 volume of hydrochloric acid (equal volumes 
of HC1 sp. gr. 1 * 17 and H 2 0). The two ingredients having been tho- 
roughly mixed by stirring, the solution is dialysed in running water for 
about eleven days. The dialyser used was 19 cm. in diameter, and the 
layer of silicic acid 4-5 cm. thick. The fluid thus obtained has a specific 
gravity of 100 '1 (about), is slightly opalescent, but transparent and 
liquid. In this condition it may be kept, for some time at least, in 
sterilized flasks. The next step is to evaporate the silicic acid down to 
3/5 to 1/2 its volume in flasks plugged with cotton- wool. 
The nutrient salts to be added are — Ammonium sulphate, 0*4 ; mag- 
nesium sulphate, 0*5; potassium phosphate, 0*1; calcium chlorate, a 
trace ; sodium carbonate, 0 * 6-0 • 9. All the sulphates are mixed together 
and dissolved in as little water as possible ; so too are the soda and 
potash salts, the extremely dilute calcium chlorate forming a third 
solution. All three are sterilized apart and thus preserved. 
The two first saline solutions are mixed with the thickened silicic 
acid and the calcium chlorate afterwards added. A few flakes from pre- 
cipitated salts are usually visible, but these do not interfere with the 
transparency of the medium, which is a fluid with the consistence of oil, 
and which, after having been poured into capsules, slowly and of its own 
accord thickens in a few hours to a jelly. 
Substitutes for Agar and Gelatin. | — Herr Marpmann says that a 
perfectly bright and clear nutrient medium having all the properties 
of agar may be prepared in the following manner, by using an alga, 
Sphserococcus confervoides , found in the Mediterranean : — 30 parts of alga 
are macerated in 2 parts hydrochloric acid and 1 litre water for two 
hours. The mixture is then washed thoroughly with water until blue 
litmus-paper no longer turns red. After decanting, there are added 
700 parts water, 40 parts glycerin, 20 parts Koch’s liquid pepton, 
2 parts beaten-up albumen. The mixture is next boiled in a steamer 
for 20 minutes, then neutralized and filtered through a syrup-filter. 
As a substitute for gelatin the author uses chondrin, which he 
extracts from rib and ear cartilage by boiling in a Papin’s digester 
under a pressure of two atmospheres. The chondrin is filtered while 
hot through an ordinary paper filter, and when cold it is found to have 
set more firmly than gelatin. Besides this greater firmness, chondrin 
possesses the additional advantage of being more slowly liquefied by 
peptonizing microbes and of not losing its consistence after prolonged 
boiling, at least not till 140° C. are reached. 
Miniature Tank for Microscopical Purposes.:}— Dr. Thomas S. 
Stevens remarks: — “Any collector from ponds and ditches, who has 
reached over the contents of a round bottle with a lens, knows how 
difficult it is to see and capture the interesting objects it may contain, 
* Centralbl. f. Bakteriol. u. Parasitenk., x. (1891) pp. 209-13. 
t Tom. cit., pp. 122-4 % Micioscope, xi. (1891) p. 156. 
