134 A MANUAL OF BACTEEIOLOGY 



barley and wheat — are easily penetrated by such agents as sublimate, 

 iodine, alcohol, ether, chloroform, and acetic acid, while silver nitrate, 

 copper sulphate, sodium fluoride, and barium chloride penetrate very 

 slowly. Taking these results as a basis, he recommends the following 

 method for the sterilization of seed : 



Wash the seeds thoroughly and allow them to soak for twelve to 

 twenty-four hours in a 5 per cent solution of silver nitrate. Follow 

 this with four washings in sodium-chloride water and then allow the 

 seeds to stand for twenty-four hours in a dilute solution of sodium 

 chloride. After this, drop the seeds into sterile bouillon and test 

 them for the presence of molds and bacteria as described above. 



lu sterilizing corn Schulow reports good results from the use of 

 1 per cent bromine solution for twenty minutes. 



Methods for growing higher plants under sterile conditions. In order 

 to grow plants in a medium free from infection, vessels of careful 

 construction are necessary. The weak point with nearly all pots built 

 for this purpose is the method of watering and of packing cotton 

 around the stem of the plant. Because of the long time required for 

 plant growth there is always danger of infecting the culture medium 

 if cotton is wrapped around the stem of the plant. To guard against 

 this it Is well to conduct this experiment in a clean room, as free as 

 possible from all outside contamination. A large variety of vessels 

 have been recommended, but many of them are so complicated as to 

 be of little practical value. Most of them are prepared either from 

 metal or from glass ; the latter have given the best results. Vessels 

 of metal — -for example, the Schulze^ pot — have many disadvan- 

 tages : first, it is almost impossible to regulate the water supply ; 

 second, in sterilization there is danger of the metal's forming com- 

 pounds poisonous to plant growth. 



Schulow " claims to have grown corn plants free from all infection 

 in glass cylinders thoroughly packed with absorbent cotton. 



The culture vessel (Fig. 44, 1) is a WoulfE's flask with three open- 

 ings. The vessel used for water is a 2- or 3-liter flask of Jena glass 

 (Fig. 44, 2) which carries a stopper with two openings. All stoppers 

 and connecting tubes must be made out of the best Para rubber. The 

 entire apparatus is made from glass and is much easier to prepare 

 than the Schulze metal pot. The large Woulff flask should hold about 

 3-4 liters and should be made from a good quality of glass. 



1 Landw. Jahrbiieher 30 : 219. 1906. 



2 Bericht. d. Deutsch. Bot. Gesell. 29 : 504. 1911. 



