54 PREPARATION OF CULTURE-MEDIA. 
VILLA 
Ruy 
Fic. 29.—Providence Health Fic. 30.—Potato-tube 
Department tube of heavy (Mallory and Wright). 
glass, with etched surface for 
writing data. These tubes are 
etched by dipping for thirty 
seconds in ‘‘ white acid.” 
last sterilization should be allowed to solidify with 
slanting surfaces. 
