SOME COMMON HOUSEHOLD INSECTS. 67 



least, twenty seconds when double sacks are used, and much can 

 be done in that time. 



Another important question connected with the use of 

 hydrocyanic acid gas is the distance it will penetrate into si 

 semi-solid mass, a sack of bran, for instance, or masses of 

 cereals held together by the webbing made by the flour moth 

 larva. 



■An apparatus used by this department to ascertain this 

 was found to be faulty, too late in the year to remedy the 

 defect, and the results of that particular experiment, therefore, 

 cannot be relied on. However, the matter was given a prac- 

 tical test by exposing a mass of webbing, over two inches thick, 

 containing live worms, pupae (and probably eggs), of the 

 flour moth to the fumes of the gas, as commonly used at the 

 above strength, and for over ten hours, the time usually occu- 

 pied in a fumigation. As far as could be observed at the time 

 everything in this mass was killed, and after three months' 

 observation of the same in our laboratory, no sign of the flour 

 moth in any stage was apparent, indicating, possibly, that this 

 g^as has a greater penetration than we had supposed. At the 

 same time this isolated experiment should not be relied upon 

 as certifying absolutely upon this point. 



While this gas in no way affects dry flour, meal, or any 

 cereals ; in fact, any food product which contains no moisture, 

 milk, butter, drinking water, or any moist food intended for 

 use should not be exposed to the fumes. Neither is it desir- 

 able that silverware, nickle or brass should come in contact 

 with it at this strength, unless coated w'ith vaseline. Further, 

 in its use, one should always bear in mind that one good whiff 

 of the fumes might prove fatal. 



SOME COMMON HOUSEHOLD INSECTS. 



There are certain very common pests of the household, 

 regarding which, the entomologist has ever recurring inquiries, 

 and at the risk of appearing to repeat information previously 

 printed by this department, we give here detailed remedies of 

 these injurious forms, without, however, describing the insects, 

 which have already been so thoroughly discussed that they 

 are generally familiar objects to every housekeeper. 



