PREPARATION OF SILICATE JELLY. 



37 



kindly to ciilture 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, c. 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 generall}- considered to be ver)' diffictdt 



to make, but by following the most recent directions of <Jmelian- 

 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 difficidt}', and to it ma}- l^e added 

 any mineral nutrient substances desired. The writer makes it in the 

 following way : 



To each 100 cc. HCl (sp. gr. 1.10° Beaume) is added drop by 

 drop 100 cc. sodium silicate (sp. gr. 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 mediinn 

 is desired, after which the jell}- 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 b}' one steaming in the 

 autoclave for 15 minutes at 1 10° 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 tlie manipula- 

 tions connected with tlie 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 man}' purposes that 

 material for making them should be on hand in ever}' lal)orator\-. 



The writer follows Kellerman in making his sacks inside of test 

 tubes. These ma}- be large or small according to what the sacks are 

 to be used for. If for dialyzing silicate jelly in some quantit}', it is 

 very convenient to make the sacks inside of test tubes 7 inches long 

 and having an internal diameter of i inch. The first tiling is to 

 prepare the collodion mixture. This is made In- dissohing soluble 

 guncotton, such as is used by pliotographers, 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 dr\- slowlv, 

 and if too much ether they are said to become Ijrittle. After some 



Fig. 35.* 



*FiG. 35. — Tollen's tlierimo-regulator for maintaining blood-serum o\'en at 80° to 90° C. Tlie 

 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 paraflin-bath chloroform replaces the glycerin. 

 Actual height, 12 inches. Chloroform and glycerin are very useful in such thermo-rcgulators be- 

 cause their coefficient of expansion is much greater than that of mercury. Toluene may also be 

 used with mercury. 



