150 



BIOLOGY AND TECHNIQUE 



Fluid Media Covered with Oil. — Erlenmeyerflasksor othervessels 

 are partially filled with glucose-bouillon over which a thin layer of al- 

 bolin or other oil is allowed to flow. The oxygen is driven out of the 

 liquid by vigorous boiling for fifteen minutes or more. 



It should be remembered whenever using this or similar methods that 

 a layer of fluid oil does not form an impermeable seal. By covering an 



alkaline pyrogallol solution with oil it 

 can easily be shown that oxygen slowly 

 diffuses through the oil into the medi- 

 um below. 



The simple exclusion of air, also, 

 is the principle underlying the culti- 

 vation of anaerobic bacteria in the 

 closed arm of a Smith fermentation 

 tube. 



Wright's Method.' — Wright has 

 described a simple and excellent 

 method for the cultivation of anaero- 

 bic bacteria in fluid media. The ap- 

 paratus necessary is easily improvised 

 with the materials at hand in any 

 laboratory. A short piece of glass 

 tubing, constricted at both ends and 

 fitted at each end with a small piece of 

 soft-rubber tubing, is inserted into a 

 test tube containing nutrient broth. 

 The upper end of the inserted glass 

 tubing is connected by the rubber 

 with a pipette passed through the 

 cotton plug in the tube. The entire 

 apparatus, plus broth, may be steril- 

 ized after being put together. When 

 a cultivation is made, the fluid in the test tube is inoculated as usual. The 

 fluid is then sucked up into the glass tubing until this is completely filled. 

 A downflow of the fluid is then prevented by placing the finger over the 

 pipette through which the suction has been made or by constricting a 

 small piece of rubber tubing attached to the upper end of the pipette. 

 The entire system of tubes is then pushed downward in such a way that 

 both pieces of rubber tubing, attached to the ends of the httle glass 



1 Wright, J. H. Quoted from Mallory and Wright, "Path. Technique," Phila., 1904. 



Fig. 34. 



Anaerobes 



Al^BOLIN. 



Cui/TIVATIGN OF 



Fluid undee 



