METHODS OF CULTIVATION. 



177 



" To introduce a culture-liquid into one of these 

 little flasks, heat the bulb slightly, break off the 

 sealed extremity of the tube and plunge 

 it beneath the surface of the liquid (see 

 Fig. 6). The quantity which enters will 

 of course depend upon the heat em- 

 ployed, and the consequent rarefaction 

 of the enclosed air. Ordinarily the bulb 

 is filled to about one third of its capacity 

 with the culture-liquid, leaving it two 

 thirds full of air, for the use of the micro- 

 scopic plants which are to be cultivated 

 in it. Fig - 5 - 



" It is best not to trust to the sterilization of the 

 culture-liquid previously to its introduction into 

 the flasks ; for, however great the precautions 

 taken, many failures would be sure to occur, as 

 the result of contamination by atmospheric germs 

 during the time occupied in the manipulations. 

 Sterilization is therefore ef- 

 fected by heat after the fluid 

 has been introduced and the 

 neck of the flask hermetically 

 sealed in the flame of an alco- 

 hol lamp. 



" This may be accomplished 

 by boiling for an hour in a 

 bath of paramne or of concen- 

 trated salt solution, by which 

 a temperature considerably above that of boiling 



water is secured. The writer is in the habit of 



12 



