PREPARATION OF SILICATE JELLY. 37 
kindly to culture media containing animal and vegetable products. It is desirable 
also for exact experiment with other organisms. It may be used in Petri dishes or 
flasks, or slanted in-test tubes. Along with some disadvantages, e. g., tendency to 
split, it has a number of valuable characteristics, not least among which is the fact 
that it enables one to offer the organism a solid substratum which is at the same 
time purely synthetic. It is generally considered to be very difficult 
to make, but by following the most recent directions of Omélian- 
ski (’99, Bibliog., XXV), and especially certain slight modifications 
introduced by Moore & Kellerman and by the writer and his assist- 
ants, it can be prepared without difficulty, and to it may be added 
any mineral nutrient substances desired. ‘The writer makes it in the 
following way: 
Toeach 100 cc. HCl (sp. gr. 1.10° Beaumé) is added drop by 
drop 100 ce. sodium silicate (sp. gt. 1.09), the mixture being stirred 
continually with a glass rod. ‘This is now placed in a collodion sack 
and dialyzed for some hours in running water. To this is then 
added in concentrated sterile form whatever synthetic culture medium 
is desired, after which the jelly is put into Petri dishes or test tubes 
and sterilized by heating for three hours in the blood-serum oven (fig. 
45) on five consecutive days at 90° C., or by one steaming in the 
autoclave for 15 minutes at 110°C. ‘The thermo-regulator shown in 
fig. 35 is useful for maintaining a constant high temperature in the 
oven. ‘The oven must also contain some water in a capsule or beaker: 
It is believed that a more detailed account of the manipula- 
tions connected with the preparation of silicate jelly will be welcome 
to many. First of all, one must have dialyzing sacks. Collodion 
sacks are much more convenient than parchment sacks, since they 
can be prepared at any time, and dialysis takes place through them 
with great rapidity. They are useful for so many purposes that 
material for making them should be on hand in every laboratory. 
‘The writer follows Kellerman in making his sacks zvszde of test 
tubes. These may be large or small according to what the sacks are 
to be used for. If for dialyzing silicate jelly in some quantity, it is 
very convenient to make the sacks inside of test tubes 7 inches long 
and having an internal diameter of 1 inch. The first thing is to 
prepare the collodion mixture. This is made by dissolving soluble 
guncotton, such as is used by photographers, in a mixture of abso- 
lute alcohol and sulphuric ether. The writer uses equal parts of 
these two fluids. If too much alcohol is used, the sacks dry slowly, 
Fig. 35.* and if too much ether they are said to become brittle. After some 
*Fic, 35.—Tollen’s thenmo-regulator for maintaining blood-serum oven at 80° to go° Cs The 
stem and bottom of the bulb contain mercury. The remainder of the bulb is filled with glycerin. 
In the similar thermo-regulator used for the paraffin-bath chloroform replaces the glycerin. 
Actual height, 12 inches. Chloroform and glycerin are very useful in such thermo-regulators be- 
cause their coefficient of expansion is much greater than that of mercury. Toluene may also be 
used with mercury. 
