RECENT WORK WITH HYDROCYANIC ACID GAS 1 99 



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 0.3 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 htindred cubic 

 centimeters of water (about 4 ounces) were added, 

 followed by an equal volume of strong sulphuric acid. 

 Thirty-six grammes (about i^ 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 The hand was at once withdrawn 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 



