130 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
cultivations in aqueous liumour. The germicidal action of the humor 
aqueus is explained conformably to the ideas of Metschnikoff, with 
whom the author is working, as being entirely due to an imperfect 
adaptation to the new medium. 
Silicic Acid as a Basis for Nutrient Media.* — Prof. W. Kiihne 
employs silicic acid as a basis for nutritive media which will bear 
prolonged exposure to high temperatures, and which have the further 
advantages of resisting the action of organisms and reagents. To make 
the compound, the author mixes, with frequent shaking, three parts of 
commercial silicate of soda (sp. gr. 1*08) and one part dilute hydro- 
chloric acid (HOI sp. gr. 1 * IT one part, and water two parts). The 
mixture is then freed, in a dialyser, from free acid and from sodium 
chloride, by suspending the dialyser for four days in a stream of 
running water. The pure solution is then condensed to a specific 
gravity of 1 * 02 by heating it in a platinum vessel. In this condition it 
contains 3*4 per cent, pure acid, is as thin as water, can be boiled, is 
miscible with alcohol, and only coagulates on addition of neutral salts. 
The nutrient addendum employed by the author was meat-extract : a 
piece of Liebig’s extract about the size of a bean is dissolved in 22 ccm. 
of water, and of this solution 0*5 to 1 ccm. is added to 4 ccm. of silicic 
acid. If it be desired to set it quickly some cooking salt must be added. 
Thus obtained the jelly is of the proper consistence, transparent as glass, 
and scarcely coloured by the meat-extract. It bears the addition of 
sugar, glycerin, &c. 
Pure Cultivations of Green Unicellular Algae. | — M. W. Beyerinck 
has obtained pure cultivations from two species, Chlorococcum proto- 
genitum Babenh. and Rhaphidium naviculare sp. n., which are frequent in 
stagnating water near Delft. The author succeeded in getting rid of the 
numerous water bacteria by the following method: — Ditch water was 
boiled up with 10 per cent, gelatin, and before setting was mixed with a 
drop of the water coloured green by the algae. In this mixture only 
those bacteria which liquefy gelatin could develope. The number of such 
colonies may be few enough not to liquefy the whole of the gelatin in 
two or three weeks. With a hand-lens the algar colonies may then be 
recognized as dark green points. These can then be distributed to fresh 
gelatin and so pure cultivations obtained. Rhaphidium was found to 
excrete a trypsinoid ferment which liquefied gelatin. It multiplied by 
fission. Chlorococcum does not liquefy gelatin, and was cultivated on 
seven different nutritive media with a neutral or slightly acid reaction. 
Development in all the seven media proceeded at about the same pace, 
but the colour of stroke cultivations was very different. 
In sterilized ditch water with 1 per cent, gelatin previously liquefied 
by pancreas, the growth advances well, and after three or four weeks 
there results a yellow fluid with a dark green sediment of Chlorococcum. 
* Zeitschr. f. Biologie, xxvii. n.s. ix. (1890) No. 1. Cf. Centralbl. f. Bakteriol. 
u. Parasitenk., viii. (1890) pp. 410-11. 
t ‘ Aanteekeningen van het verhandelde in de sectie-vergaderingen van het 
Provinciaal Utreehtsch Genootscbap voor kunsten en wetenschappen gehouden 
den 25 Juni 1889/ pp. 85-52. Cf. Centralbl. f. Bakteriol. u. Parasitenk., viii. 
( 1890) pp. 460-2. 
