CULTURE VESSELS 



29 



Culture vessels. 



Vessels of various patterns are used for culture media, and these will be 

 described as occasion for their use arises. In this chapter a description of 

 those most commonly used for the growth of aerobes only will be given. 



1. Ordinary test-tubes, but without lips, are in constant use (fig. 30) ; they 

 must be plugged with wool as already described. 



2. Erlenmeyer flasks conical glass vessels with a flat bottom (fig. 31) and 

 of different sizes [and Jena flasks,] are also in frequent use. Ordinary small 



&>3 



FIG. 30. Culture tube 

 plugged with wool. 



FIG. 31. Erlenmeyer flask. 



medicine bottles of 30 to 50 c.c. capacity can be used in many cases. What- 

 ever be the shape of the vessel it must be plugged with wool, and as a further 

 protection a paper cap is useful (vide p. 4). 



3. Small vessels capable of holding 30 to 50 grams and known as Pasteur's flasks, are 

 also in frequent use [in France]. The mouths of these flasks are generally closed by 

 means of an hollow ground-glass stopper fitting a similarly ground-glass surface on the 

 neck of the flask, and having a small orifice above, which must be plugged with wool. 

 This method of plugging effectually preserves the contents of the flasks from contamina- 

 tion, but has the disadvantage of being very fragile, and the glass cap is often broken in 

 the flaming process preliminary to opening the flask. 



It is better to cover the mouth of the flask with a small paper hood (this can be done 

 by enveloping the neck in a small strip of filter paper and tightly screwing the projecting 

 part into a point). It is even simpler to plug the flasks with wool in the same way as 

 test-tubes are plugged. 



Miquel's flask is merely a conical form of Pasteur's pattern. 



Prevention of evaporation. 



Evaporation readily takes place through a wool plug, and if a medium especially 

 a solid medium such as potato, serum, agar, etc. be stored or incubated for a 

 long time, the amount of evaporation is likely to be excessive. To avoid this, the 

 mouth of the vessel may be closed with an india-rubber cap. This must be 

 sterilized before use, because when the cap is slipped over the mouth of the tube or 

 flask the air within being saturated with aqueous vapour will soon make the wool 

 plug moist, and then any organism on the inner surface of the cap will ultimately 

 grow through the moist plug and contaminate the contents. 



