COLLODION SACS 175 



By this method, organisms can be cultivated in the body, and at the same 

 time be protected from phagocytes. The thin walls of the collodion sacs, 

 while allowing osmotic changes to take place which alter the composition 

 of the medium in the sacs and permit the toxins secreted by the organisms to- 

 diffuse into the tissues of the animal, prevent cells (micro-organisms and 

 phagocytes) passing through. This method has many applications in bac- 

 teriological work. 



All the soluble products of micro-organic metabolism dialyse more or less 

 through the walls of collodion sacs, but they do not pass through in toto. The 

 collodion membrane does not act as a perfect filter, so that some toxins pass through 

 only with difficulty and very slowly (Rodet and Guechoff). The immunizing 

 substances seem to pass through first (Crendiropoulo and Ruffer). 



(a) Method of preparing collodion sacs. Have ready (1) a wide-mouthed 

 bottle containing collodion, free from castor oil, and of a medium syrupy 

 consistence, (2) some small glass tubes of 5-6 mm. internal diameter, (3) some 

 small conical india-rubber plugs, (4) a test-tube carefully calibrated and not 

 enlarged at its lower part, (5) some silk thread. 



Collodion containing castor oil [collodium flexile B.P. ] may be used instead of 

 ordinary collodion but such sacs are not so transparent, though they are more 

 elastic and stronger than the others. 



1. Rotate the lower end of the test-tube regularly on the sloping surface 

 of the collodion and prolong the contact according to the thickness which 

 the layer of collodion is to have. 



2. Remove the tube from the collodion and continue turning it between 

 the fingers for about a minute. Then let the layer of collodion dry for a 

 few minutes until it is of a semi-liquid consistence. 



3. With a scalpel cut round the layer of collodion near its upper end and 

 separate the sac from the tube, thus : Free the upper end of the sac with the 

 thumb nail, turn it back like a glove finger and gradually peel it off. This 

 must be done slowly. [Dipping in methylated spirit softens the collodion 

 and makes it strip easily.] 



4. Distend the sac by blowing into it. A sac may be made to hold from one 

 to several cubic centimetres according to the particular requirements of the 

 experiment. 



5. Fit a piece of small glass tubing into the open end of the sac, fasten it 

 on with several turns of silk thread and cover the silk with a little collodion. 

 Fill the sac with water and suspend it by a thread in a bottle or test-tube 

 containing a little water. Plug the vessel with wool. Place the india-rubber 

 plugs in a flask plugged with wool and containing a little water. Sterilize 

 at 115 C. in the autoclave. 



All these manipulations are delicate and take a long time, and it will often be 

 advantageous to use the collodion sacs which can now be bought in the shops. 



6. Take each sac out of the bottle with a pair of sterile forceps and 

 transfer it to a sterile dish covered with paper. Suck up the water out of 

 the sac with a pipette and replace it with broth sown with the organism under 

 investigation. 



7. Close the opening of the tube with an india-rubber plug picked up with 

 sterile forceps, and cut it off short close to the tube with a sterile scalpel. 

 Dehydrate the plug in absolute alcohol and cover it with several layers of 

 collodion. 



Notes. (i) Bertarelli has recommended a method which considerably simplifies 

 that just described. In Bertarelli' s method, the free end of the piece of glass tubing 

 to which the sac is affixed is drawn out beforehand so that the free end is fine and 



