Spojx-C^iltnre. 



113 



must be sterilized by heat ; and after the nahrlosung has 

 been introduced, the two ends of the tube arc closed by- 

 cotton wool ; this allows free access of air, but filters out 

 any germs that may be floating in it. 



Or the culture may be made in a hanging-drop cell 

 made of lead tubing, in the sides of which two holes have 

 been cut (Fig. 13). I have found it most convenient to 



Fig. 13. — Hanging-drop culture cell, made of lead tubing, with two holes for the admis- 

 .sion of air ; when in use with nahrlosung these openings are closed with cotton wool. 



wrap cotton wool round the cell, and to hold it in its place 

 by a small elastic band. These cells require to be sterilized 

 by washing w'ith a weak solution of corrosive sublimate. 



