CULTIVATION IN COLLODION CAPSULES. 211 



drop or two of melted agar along each side of the agar 

 block where it is in contact with the cover-slip. This 

 seal hardens at once, preventing slipping of the block. 

 Place the preparation in the incubator again for 

 five or ten minutes to dry the agar seal. Invert this 

 preparation over a moist chamber and seal the cover- 

 slip in place with white wax or paraffin. Vaselin 

 softens too readily at 37 C., allowing shifting of the 

 cover-slip. The preparation may then be examined at 

 leisure." 



Aerobic bacteria receive sufficient oxygen by dif- 

 fusion, and for anaerobic bacteria it will suffice to 

 expose the block to the action of alkaline pyrogallic 

 solution. 



CULTIVATION OF BACTERIA IN COLLODION CAP- 

 SULES. The use of small capsules of collodion for the 

 cultivation of bacteria was first introduced by Metschni- 

 koff, Roux, and Salembini. The bacteria under study are 

 placed in a small collodion capsule containing a nutritive 

 fluid, as bouillon, and, after sealing the capsule, it is 

 placed in the peritoneal cavity of an animal. Under 

 these conditions the bacteria are protected against the 

 phagocytic action of the body-cells, though the metabolic 

 products of the bacteria diffuse out and act upon the 

 animal. 



Collodion capsules are easily constructed by the method 

 of McCrae, as follows : Fuse a short piece of narrow, 

 thin-walled glass tubing into the top of a No. 12 gelatin 

 capsule. This is done by simply heating one end of the 

 glass tubing in the flame of a Bunsen burner and push- 

 ing it through the top of the capsule. Both halves of the 

 gelatin capsule are now fitted together, and the closed 

 capsule is dipped repeatedly into liquid collodion. When 



