1903] Robinson, — Insecticides used at Gray Herbarium 241 
low dishes of carbon bisulphide. About six or eight ounces of this 
were employed for each fumigation and the specimens were left in at 
least thirty-six and usually forty-eight hours. The effects were 
entirely satisfactory, so far as sure death to the insects was con- 
cerned ; but it was soon found necessary to increase greatly the capac- 
ity of the apparatus, and four other cans, each capable of holding 
about two thousand sheets of specimens were installed. ‘These were 
constructed upon the same plan, but the shallow pigeon-holes for the 
insertion of the sulphide were arranged at the top instead of the bot- 
tom, on the theory that the vapor of carbon bisulphide, being some- 
what heavier than air would diffuse more effectively downward than 
upward. In regard to this point, it may be said that diffusion, 
although of unequal rate would doubtless occur effectively in both 
directions, and that theoretically it would be best to insert the sul- 
phide somewhere about a fourth of the distance from the top to the 
bottom. 
Working with the apparatus above described the staff of the her- 
barium fumigated the entire organized collection and the stored bun- 
dles of unworked specimens. Although the mere manual labor of 
the undertaking was considerable, the results were very repaying. 
For some months the herbarium was, so far as could be ascertained, 
entirely free from insects. After a year or so, a rare and sporadic 
reappearance of the herbarium beetle, led to a refumigation of con- 
siderable portions of the collection. Although since the use of the 
carbon bisulphide method, the number and depredations of the her- 
barium insects has certainly been reduced by 95 %, it has been 
thought best to employ in conjunction with this treatment some other 
precautions. An entomologist who was consulted said that the book- 
louse could be successfully kept out of any case by the use of cam- 
phor, naphthalin or, in fact, any agent producing a strong odor. In 
accordance with this suggestion flake naphthalin was purchased in 
large quantity and liberally sprinkled in each pigeon-hole of the her- 
barium cases. This was done immediately after the cases had been 
carefully cleaned while the specimens had been removed for their 
treatment with carbon bisulphide, the naphthalin being left in the cases 
when the herbarium specimens were replaced on the shelves. At the 
outset there was considerable scepticism regarding the value of naph- 
thalin, but there is now good reason to believe that by discouraging a 
new immigration of insects, it is a useful adjunct to the carbon bisul- 
