METHODS OF CULTURE AND OF EXAMINATION. 91 



chamber, and one of these plates, grasped carefully at its 

 edges with the fingers, or, better, with forceps sterilized in 

 the flame, is placed upon a plate covering a dish filled with 

 ice. Over this plate, in order to reduce the possibility of 

 aerial infection to a minimum, is placed a bell-glass that 



Fig. 21. Leveling and cooling apparatus. 



has been immersed in mercuric-chlorid solution. The entire 

 apparatus may with advantage be mounted upon a leveling 

 device. (Figs. 21, 22.) The cotton stopper is now quickly 

 removed from the original tube, the lips of which are passed 

 through the flame and are briefly permitted to cool, and 

 after removal of the bell-glass the contents of the tube are 

 poured upon the center of 

 the rectangular plate, and are 

 distributed evenly with the 

 lips of the tube, care being 

 taken to leave a free space 

 of one centimeter at the bor- 

 ders of the plate. Some of 

 these glass plates are pro- 

 vided, at a distance of orre 

 centimeter from their bor- 

 ders, with a wall of enamel 

 about one millimeter high, 

 for the purpose of preventing 



Fig. 22. Complete leveling apparatus 

 for pouring plate-cultures, as taught by 

 :h. 



Koct 



overflow of the gelatin. The 



gelatin solidifies rapidly upon the ice base after the bell- 

 glass is replaced, and the finished plate is now placed upon 

 a glass shelf or bench in a crystallizing dish, which is con- 

 verted into a moist chamber by the insertion of bibulous 

 paper moistened with a solution of mercuric chlorid. The 



