and Laboratory Methods. 



1747 



about 10 minutes, close the rubber tubing 

 at (D) by means of a clamp, cut the tubing 

 about two cm. above the clamp and fill the 

 end with glycerin. The freedom of the 

 apparatus from oxygen can be tested as 

 follows : Bring a burning match close to 

 the glycerin in the bowl where the bubbles 

 escape. If the latter burn regularly and 

 without explosion, the apparatus may be 

 considered oxygen-free. In order to ob- 

 tain access to the petri dish when the 

 culture has developed, carefully and slowly 

 raise the bell jar on one side, allowing 

 small bubbles of air to enter. This will 

 prevent the glycerin from spattering into 

 the culture. 



Botkhi's apparatus (Fig. 21) is a modification of that of Blucher. It contains 

 a glass dish (D) 20 to 25 cm. in diameter (much the same as those used for 

 potato cultures). In the dish (D) stands a wire support for the petri dishes, 

 which are covered by bell jar (B). The latter has a diameter about three cm. 

 smaller than dish (D). It does not touch the bottom of (D) directly, but it rests 

 on a cross band of lead (L) one cm. in thickness. U tube (U) is a thin rubber 

 tube ; its lumen contains a fine, soft, and flexible copper wire. Opposite tube 

 (U) there is another similarly constructed rubber tube (F) leading from the 



Fig. 20 



Fig. 21. 



interior of the bell jar into a wash bottle (W) containing water and closed by a 

 doubly perforated rubber stopper ; the second perforation carries a glass tube 

 continuing into a rubber tube and closed by a clamp (C). 



Method. — Disinfect the interior of the apparatus by washing with a solution 

 of sublimate and drying with alcohol and ether. Sterilize the wire support in the 

 flame. Prepare the culture plates in the ordinary way and place them on the 

 wire stand. Pour a layer, three cm. high, of paraffin liquidum, preferably Buch- 

 ner's mixture (1 part glycerin to 3 parts water) into dish (D). Insert the U tubes 



