1754 



Journal of Applied Microscopy 



saturates with a concentrated solution of pyrogallic acid. This absorbing mate- 

 rial he fits into the cover of a deep petri dish. 



Method. — Weigh 4-5 gms. of dry pyrogallic acid into a small beaker, add a 

 50 per cent, solution of potassium hydroxid, drop by drop, and shake until the 



Fig. 84. 



pyrogallol is perfectly wet. In a few minutes it will be dissolved. The less 

 potassium hydroxid used the greater is the absorbing power of the solution. 

 Drop the solution of alkaline pyrogallol upon the mat of cardboard, felt or cel- 

 lulose. Do not saturate the absorbing material completely, otherwise some of 

 the reagent might run down into the medium. Invert the cover containing the 

 absorbed reagent over the culture plate, which has previously been filled with 

 the inoculated medium. Seal the space between the rim of tlie cover and that 

 of the plate with a mixture of white wax (12 parts) and beef tallow (lOU parts) 

 and finally cover the seal with a firm and well fitting rubber band. 



For single tube cultures Smith* uses the following de- 

 vice : Into one end of a large U tube insert a small test 

 tube containing the inoculated culture medium. Invert 

 the other end over a small slender flask or vial containing 

 a strongly alkaline solution of pyrogallol and standing the 

 ends of the tube in a dish containing oil. 



The writer modifies Smith's method as shown in Fig. 

 35. Into one end of a large U tube place about three 

 grams of dry pyrogallic acid and three grams of sodium 

 hydrate. Close this end with a rubber stopper and pour 

 about 15 c. c. of water into the other end (b) holding the 

 U tube so that the water all escapes into the branch (a) 

 containing the reagents. Now insert in the second branch 

 (b) a small test tube (c) containing the inoculated medium 

 and a loose cotton plug. Close this end of the U tube 

 with a rubber stopper and stand the U tube in a beaker 

 (d) containing mercury or glycerin. Good results were 

 Pj^ .,- obtained by this method. 



*The method of Dr. Erwin F. Smith, Department of Agriculture, Bureau of Plant Industry, 

 Washington, D. C, has not as yet been published. 



