METHODS OF CULTIVATION. 171 



have an opportunity to germinate, and are killed 

 by the subsequent heating. The writer has not 

 been successful in sterilizing milk by this method, 

 and has recently lost the greater portion of a batch 

 of tubes containing blood-serum, carefully treated 

 according to Koch's directions, from the develop- 

 ment of Penicillium glaucum upon the surface of the 

 jellified serum. The spores of this fungus were 

 evidently very abundant in the laboratory at the 

 time the serum was introduced into these tubes, 

 which had been well sterilized by heat and were 

 thoroughly protected by cotton wadding tied over 

 the mouth of each, with the additional precaution 

 of covering this with a piece of sheet-caoutchouc 

 secured by a rubber band. No doubt the unusual 

 abundance of the spores of Penicillium was due to 

 the disturbance of the dust upon a lot of books 

 which were taken down from an upper-shelf by 

 my assistants, shortly before the blood-serum was 

 decanted and introduced into the culture-tubes. 

 According to Pasteur, the spores of Penicillium 

 and other common mucedines are not destroyed 

 by a temperature of 120 to 125 C (248-257 F.), 

 in the absence of moisture. 



Culture Tubes and Flasks. Glass tubes or flasks 

 are used as germ-proof receptacles for the steril- 

 ized culture-fluids mentioned. Ordinary test-tubes 

 are commonly employed, and are useful for many 

 purposes. They should be thoroughly heated in 

 an oven, or in the flame of an alcohol lamp, just 



