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MEDICAL BACTERIOLOGY 



Collodion Sacs. The use of the collodion sac has recently become 

 very common and deserves description as one of the necessary labor- 

 atory procedures. The difficulty in making these sacs has been 

 largely overcome by recent methods. One of these is the following : 

 Small-sized test-tubes are selected. Thick collodion is then poured 

 into the tube to a depth of two inches. The collodion is then 

 poured out along one side of the tube into another tube and from this 

 one to another and so on until the required number is obtained. The 

 desired length of the sac can be secured in all of the tubes by tipping 

 and rolling them, thus bringing the collodion into contact with the 

 glass to the proper height. As the tubes are coated they are placed, 

 mouth down, in a wire basket or test-tube rack as indicated in Fig. 

 34, 1) . In this way the extra collodion drains off and free access of 

 air dries and hardens the collodion, leaving a thin coat covering the 

 inner surface of the tube. The thickness of the coat depends on the 

 consistency of the collodion. A ten per cent, collodion, in equal 

 parts of alcohol and ether, makes a sufficiently thick coat for ordi- 

 nary purposes. The drying may be stopped at any point by filling 



Fig. 31. Preparation of Collodion Sac: 1, Tube inverted to allow the extra collodion 

 to drain off and the film to air-dry. 2, Sae ready for sterilization; (A) Surgeon's knot; 

 (B) Ends of cord; (C) Tongue of collodion. 3, Sao ready to be inoculated into animal. 



the tube with water and after standing a few minutes the collodion 

 shrinks and the sac may be easily removed. The sacs are then filled 

 from one-fourth to three-fourths full with bouillon. They are then 

 immersed in a test-tube of the medium. The sacs are held in posi- 

 tion in the test-tube by means of the tongue formed by the collodion 

 flowing out of the tube. This tongue is folded over the lip of the 

 tube. (Fig. 34, 2, C.) Before, however, the sac is put into the test- 

 tube a piece of cotton or silk cord is placed around the sac near the 



