Collodion sacs for aërobic and anaërobic bacterial cultivation

Abstract

The collodion sacs demonstrated before this society a year ago, 1 while suitable for intraperitoneal implantation are not so well adapted to microbic cultivation in vitro. We have therefore been making sacs of 5-10 c.c. capacity in test tubes lined with a dried film of gelatin 2 which softens in warm water and permits the easy removal of the collodion membrane. The sac is slipped on to a supporting glass tube, inserted into one limb of a V-shaped tube, open at both ends, and sealed in place with a collar of rubber tubing. Sac and V tube are partly filled with water, plugged with cotton and sterilized in the autoclave. Shrinkage during sterilization may be avoided by maintaining a pressure of 10-12 cm. of water in the sac. The sac may even be expanded by this method, but its permeability apparently is not thereby increased.

After sterilization the chosen medium is placed within the sac, and dialysis of nutritive and growth-promoting substances occurs into the surrounding fluid, which is accessible for inoculation through the other limb of the V tube. For anaärobic cultivation both medium and dialysate may be layered with vaseline. The vaseline seal excludes oxygen, but also retains C0₂ and may therefore tend to a more rapid acidification of the medium.

Osmotic pressure adjustments take place automatically by changes in the levels of medium and dialysate. With experience the approximate osmotic pressure of a given medium may be anticipated and the passage of water into the sac may be avoided by filling it with medium to a higher level.

These sacs were prepared especially for use with the Smith Noguchi fresh tissue medium. This medium, consisting of ascitic fluid or dilute serum and a fragment of fresh rabbit kidney or testicle is placed within the sac, in the dialysate of which we have grown subplants of T. pallidurn, S. microdentiurn and Bacterium pneumosintes.