CULTIVATION ON LIQUID MEDIA 97 



apparatus. The openings are laterally situated and are plugged with 

 india-rubber corks, each of which is perforated by a piece of glass tubing. 

 To each of the latter a piece of red rubber pressure-tubing is attached at its 

 outer end. When the apparatus is to be closed, the tubing is compressed by 

 screw clips and a piece of glass rod tightly fitted into its distal end. 



[1. On the ground-glass plate stand a shallow glass vessel 3-4 inches deep, but 

 having as large a diameter as will permit of the bell jar being placed over it. 



[2. Place about J oz. of pyrogallol in the bottom of the vessel. 



[3. Place the tubes in a suitable receptacle, and stand the latter on a glass 

 tripod in the vessel containing the pyrogallol. 



[4. Grease the lower flanged end of the bell jar with unguentum resinae, 

 and press it firmly down on to the ground-glass plate in such a way that 

 the long tube passes into the shallow glass vessel. 



[5. Aspirate about 40 c.c. of strong potash solution (30-40 per cent.) into 

 the vessel. Then screw up the clips as tightly as possible, and plug the distal 

 end of the tubing with glass rod. 



[6. Incubate. 



[7. To remove the tubes, withdraw the pieces of glass rod, gently unscrew 

 the clips, slide the bell jar off the glass plate and lift out the receptacle 

 containing the tubes.] 



[I. Bullock's method modified. Method recommended. The use of pyro- 

 gallol and potash is as a rule supplemented by exhaustion and washing 

 with hydrogen. 



[1. Proceed as in 1, 2, 3 and 4 above. 



[2. Attach the glass tube which passes just inside the apparatus to a 

 water pump connected with a manometer, and the other tube which dips 

 into the vessel to a cylinder of hydrogen. 



[3. Exhaust the vessel. 



[4. Turn on the hydrogen tap and pass a slow stream of gas until the 

 manometer falls to zero. Unless this be carefully done the pressure of 

 hydrogen will lift the bell jar. 



[5. Turn off the hydrogen. Exhaust again. 



[6. Wash with hydrogen again, and again exhaust. 



[7. Screw up both clips as tightly as possible. 



[8. Disconnect the bell jar from the water pump and also from the cylinder 

 of hydrogen. 



[9. Connect the tubing that dips into the vessel to a beaker containing a 

 40 per cent, solution of potash in water. Gently loosen the clip and allow 

 40 c.c. or so of the solution to enter the bell jar, being careful to allow no 

 air to enter. Screw up the clip. 



[10. Insert a tightly-fitting piece of glass rod into each piece of india-rubber 

 tubing on the distal side of the clip. 



[11. The vessel is now ready to be placed in the incubator.] 



[The security of the joints should be tested on the following day, or even later 

 on the same day. To do this, attach the same piece of tubing as before to the 

 manometer, turn on the water pump to exhaust the rubber connexions, etc., and 

 then loosen the screw clip. If the apparatus is securely fastened the mercury 

 should remain at the same level as when the bell jar was exhausted.] 



J. Legros' method. Method recommended. By this method the air is 

 excluded from the medium by means of a layer of vaseline oil. Pour 

 sufficient oil into the culture-tube to form a layer 5-10 mm. deep on the sur- 

 face of the medium. Plug with wool, and autoclave. Sow in the ordinary 

 way through the layer of oil. 



