694 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
quantity of ether, which is removed by heating the fluid, in flasks 
plugged with cotton wool, up to 50° and then placing it under an air 
pump whereby tlie ether is evaporated in 3-4 hours. This sterile and 
fat-free milk may be used as a cultivation fluid or rendered solid as 
follows : — Two parts of this unfatted milk are mixed with one part of a 
3-4 per cent, agar solution at a temperature of 50° and then placed in 
test-tubes. The tubes should then be placed in an incubator for a few 
days in case any air germs may have infected them. Made in this way 
milk-agar is quite transparent pale yellow, and with reflected light 
faintly opalescent. 
Dr. R. Wollny* has devised a method whereby many of the incon- 
veniences unavoidable in the customary methods of sterilizing cultiva- 
tion media are obviated. He has found ordinary ethyl-ether to be 
an excellent agent for this purpose and the subsequent removal of which 
does not present the slightest difficulty. Not only does it not affect the 
chemical composition of the fluids on which it exerts a sterilizing 
influence, but it also aids in removing from them fatty matters usually 
so detrimental to cultivation media. 
The juice of finely chopped-up meat, fish, liver, potatoes, &c. (or 
blood, urine, milk), which has been expressed or extracted with water, is 
mixed with 10 per cent, of ether and placed in a closed vessel. If any 
acetic acid be present from the oxidation of the ether it must be neutra- 
lized with an alkali. The fluids are then cleared by decantation or fil- 
tration or may be thickened by the addition of 3 per cent, agar solution 
or 15-20 per cent, gelatin solution. The ether is then removed by 
placing the nutrient fluid in a flask closed with cotton- wool ; the flask is 
next heated to 35°-40° and placed under the receiver of an air-pump. 
The fluid is then ready for use, although at this stage it may be mixed 
with agar-gelatin or soda solution. None of the albumen is lost and it 
is perfectly unchanged. 
Many nutrient solutions prepared in this way, such as meat, liver, 
potato, are of a rather dark colour, but they are usually quite trans- 
parent enough for cultivation purposes; others, such as extracts of 
intestine, fish, milk, are perfectly clear and transparent. 
In preparing milk by this method it is necessary to use a larger 
quantity of ether in order to completely remove all the fat, and also to 
add caustic soda solution if a perfect and transparent solution is 
desired. 
Growth of Bacteria on Acid Nutritive Media.* — The most prevalent 
notion as to the reaction of cultivation media is, says Herr G. Schliiter, 
that an alkaline or neutral reaction is almost absolutely necessary. In 
order to show that an acid reaction is not so very inimical to bacterial 
growth, the author made a series of experiments with some of the best 
known bacteria such as Bac. typhosus, Bac. anthracis , Staph, pyogenes 
aureus , Friedlaender’s pneumonia-coccus, the coccus of erysipelas, and 
others. The basis of the medium was ordinary gelatin or isinglass 
mixed with 1*25 grm. pepton, 1*25 grm. NaCl, and 250 grm. water. 
To this mixture were added acids (lactic, tartaric, citric, acetic, hydro- 
* Centralbl. f. Bakteriol. u. Parasitenk., xi. (1892) pp. 752-6. 
t Tom. cit., pp. 589-98. 
