The Fermentation Tube 189 



is given half size in the plate (fig. i). It is essentially a tube bent 

 at an acute angle, closed at one end and enlarged at the other into 

 a bulb. At the angle the tube is more or less constricted. To it a glass 

 foot is attached so that the tube may stand upright. For the sake of 

 uniformity, the closed portion of the tube will be denominated "closed 

 branch," the open portion, "the bulb," the intermediate narrow, bent 

 portion the "connecting tube." 



In the construction of this simple bit of apparatus several points must 

 be borne in mind. The bulb should be large enough to receive all the 

 fluid contained in the closed branch, for in some kinds of fermentation, 

 the gas production drives out all the fluid from the closed branch. The 

 cotton-wool plug must not be moistened under such circumstances 

 otherwise the purity of the culture is imperilled. If the bulb is suffici- 

 ently large this difficiilty will not arise. The connecting tube should 

 not be too small, for then the filling and emptying of the closed branch 

 becomes very tedious. Nor should it be too large, otherwise the anae- 

 robic properties of the fluid in the closed branch, to be discussed farther 

 on, may be lesseff"ective. Lastly the angle formed by the two branches 

 of the tube must not be too acute otherwise the tube must be tilted so 

 much during the transferrence of the fluid from the bulb to the closed 

 branch that there is danger of its moistening the plug or even running 

 out of the bulb. Since the closed branch is not accessible to cleansing 

 with a brush it is advisable to fill the tube after use with the ordinary 

 cleaning mixture (bichromate of potash and sulphuric acid) and allow it 

 to stand undisturbed for some days. 



The filling of the tube with culture fluid does not give rise to any 

 difficulty. The fluid is poured into the bulb until this is about half full. 

 The tube is then tilted until the closed branch is nearly horizontal so 

 that the air may bubble up through the connecting tube and permit the 

 fluid to enter the closed branch. When this has been completely filled, 

 enough fluid should be added to cover the lowest expanding portion of 

 the bulb. If the tubes are likely to remain unused for a month or 

 longer it is best to add fluid until the bulb is half full to allow for evap- 

 oration. 



The sterilization requires a few suggestions. This is best done in a 

 steamer like the ' Arnold ' for the tubes can be placed directly on the 

 perforated plate in the bottom of the steam chamber. If a steamer is 

 not at hand, an ordinary tin or granite-ware pail having a tight cover 

 may be used. Enough water is poured in to form a shallow layer. To 

 prevent the upsetting of the tubes by the ebullition I have been in the 

 habit of placing them, three or four together, into perforated cups 

 which are placed directly on the bottom of the pail. Steaming or boil- 

 ing on three consecutive days is sufficient for complete sterilization. 

 During the boiling the tension of the aqueous vapor in the closed branch 



