4 Department Circular 294, U. S. Dept. of Agriculture. 
driven out the mite trouble soon subsides. As is well known, com- 
plete control of rats is extremely difficult. This is especially true 
-where only sporadic and individual efforts are put forth against 
them. In the case of the infestations in north Texas a continuous 
and energetic warfare against the rats has been recommended, and 
along with this the cleaning out of all débris and nests and thorough 
spraying with kerosene. On floors a mixture of anthracene oil, 1 
part, and kerosene, 2 parts, has been advised and used with success. 
This apparently destroys and repels the mites for several days. For 
the spraying of cabinets, desks, and shelves, a fine mist spray of 
gasoline appears to give temporary relief. 
Undoubtedly fumigation with hydrocyanic-acid gas is one of the 
most effective methods of procedure, especially if rats can be excluded 
following the treatment. ‘This was tried in a motion-picture house 
in May, 1922. Up to September 1 of that year there was no recur- 
rence of the mite trouble, although the rats had reappeared in moderate 
numbers. In this case the standard proportions of the chemicals 
were employed, using 10 ounces of sodium cyanid (96-98 per cent) for 
each 1,000 cubic feet of contained space. As hydrocyanic-acid gas is 
extremely poisonous, fumigation should be conducted only by those who 
are thoroughly informed regarding the process and who use the greatest 
care. 
Pyrethrum when fresh gives relief if used very frequently, but 
in all cases it seems essential to get at the nesting places of the rats 
to secure satisfactory control. 
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