1903] Robinson, — Insecticides used at Gray Herbarium — 239 
nent more or less shellac-like coating over the specimens, even when 
very thin, affects the appearance of the surface. 
A final annoyance in connection with the sublimate treatment 
arises from the circumstance that the substance is a violent poison 
to human beings as well as to insects. I am not aware that any case 
is on record of a person having been injured or even greatly annoyed 
by the use of corrosive sublimate in connection with an herbarium, 
although a physician once told me that he had experienced some irrita- 
tion of the eyes while poisoning plants in this manner. However, 
although the danger to the amateur, whose herbarium work is confined 
to scattered hours of leisure, may be so slight as to be negligible, the 
question becomes more serious in a great herbarium in which an 
assistant would have to be engaged more or less continuously in such 
employment. The fact that corrosive sublimate is not a volatile sub- 
stance doubtless much diminishes the danger, but in this connection 
it is to be remembered that during the changing of the driers and 
mounting of the plants subsequent to the dipping, many minute parti- 
cles from the plants and driers are necessarily detached, forming a 
dust saturated with sublimate, which in this way must, to a consider- 
able extent be inhaled by a person carrying on the work. 
At the Gray Herbarium, however, it was not the difficulty, expense 
or even the danger (against which some expedients could probably 
be devised), which led to the abandonment of corrosive sublimate as 
an insecticide. It was its inefficiency. After many years experience 
with it Dr. Gray, annoyed by the poor results, declared with con- 
scious hyperbole that the more the sublimate was used, the more 
insects came, — that they throve and grew fat on it. 
About 1885 the sublimate was replaced at the Gray Herbarium |. 
by an alcoholic solution of acetate of arsenic. All plants added to 
the herbarium were dipped in this in the same way as above 
described for the sublimate solution. The acetate was selected from 
several salts of arsenic because of its deliquescent character, in con- 
sequence of which it was believed that it would be less likely to be 
detached as dust and render the atmosphere of the herbarium rooms 
unwholesome. This method was followed until 1890, when it was 
found on medical examination that two of the assistants, who had 
been suffering from some unknown irritation and general debility, 
had absorbed considerable quantities of arsenic, which in one 
instance had produced a temporary irritation of the kidneys. The 
