96 MANUAL OF BACTERIOLOGY. 



are able to diffuse through the collodion, while the animal's fluid 

 may pass into the sac to nourish them. These capsules were 

 originally made by dipping the round end of a glass rod into 

 collodion repeatedly. McCrae's method* is easier and more 

 satisfactory. (Fig. 36.) 



A piece of glass tubing is taken, and a narrow neck drawn on it near one 

 end. This end of the tube is rounded in the flame, and the body of a gelatin 

 capsule is fitted over it, while still warm, so that the gelatin may adhere to 

 the glass. The capsule is now dipped into 3 per cent, collodion, covering 

 the gelatin and part of the glass. It is allowed to dry a few minutes, and is 

 dipped again. In all, two or three coatings may be given. The capsule is 

 filled with water and boiled in a test-tube with water. The melted gelatin 

 is removed with a fine pipette. The capsule is partly filled with water or 

 broth and sterilized. The capsule may now be inoculated. The narrow part 

 of the neck must then be sealed in the flame, taking care that the neck be dry. 

 The sealed capsule should be placed in bouillon for twenty-four hours. No 

 growth should occur outside the capsule if it is tight. It may now be placed 

 in the peritoneum of an animal. 



A method for making collodion sacs recommended by Gorslinef consists 

 in the use of a glass tube, the lower end of which is rounded and closed, except 

 a small hole, which is temporarily filled with collodion. This tube is dipped 

 in collodion and dried, as above. It may now be filled with water. By 

 blowing at the opposite end, the pressure through the hole in the bottom of 

 the glass tube will cause the capsule to loosen so that it comes away easily. 



There are also various other methods recommended for making collodion 

 sacs. 



* Journal of Experimental Medicine. Vol. VI., p. 635. 

 t See Contributions to Medical Research. Dedicated to Victor C. Vaughan. 

 1903. 



