RECENT WORK WITH HYDROCYANIC ACID GAS I99 
of the men engaged in hoeing, or through the agency 
of the wind or of birds. 
Preliminary experiments indicate that at least forty 
minutes’ exposure to the cyanide fumes was necessary 
to ensure the complete destruction of the mites. 
Shorter periods were apparently successful at a first 
inspection, but a further examination showed that 
many individuals recovered after twenty-four hours. 
Doses of cyanide varying from 0.05 gramme to 0.4 
gramme per cubic foot were tested. A minimum of 
0.2 gramme per cubic foot was satisfactory. A 
stronger dose than o.3 is not desirable. 
Cuttings and young bushes.—About 2,000 diseased 
bushes intended for planting were treated January 3d 
as follows: They were tied in bundles and placed in a 
heap on the ground. Four hurdles were arranged as 
a support, and the whole covered with a waterproof 
cloth. A small vessel was placed on the ground in 
the center of the heap of bushes. One hundred cubic 
centimeters of water (about 4 ounces) were added, 
followed by an equal volume of strong sulphuric acid. 
Thirty-six grammes (about 144 ounces) of commercial 
98 per cent. potassium cyanide was wrapped in thin 
blotting-paper and dropped cautiously into the vessel 
of acid and water. The hand was at once withdrawn 
and the canvas carefully pressed down all round with 
lengths of timber. After one hour the cloth was 
removed and the operation was complete. 
Mr. Theobald conducted a systematic microscopic 
analysis of the treated buds, and established the fact 
that this treatment had destroyed all the mites. The 
bushes were planted out in disease-free soil and were 
