m a farm on Staten Island, who had adenoids in
his nose and breathed through his mouth, which was always wide open,
was looking up at this pipe, at a small leak of mercury, when the rubber
tube came off and probably two pounds of mercury went into his mouth and
down his throat, and got through his system somehow. In a short time he
became salivated, and his teeth got loose. He went home, and shortly his
mother appeared at the laboratory with a horsewhip, which she proposed
to use on the proprietor. I was fortunately absent, and she was
mollified somehow by my other assistants. I had given the boy
considerable iodide of potassium to prevent salivation, but it did no
good in this case.

"When the first lamp-works were started at Menlo Park, one of my
experiments seemed to show that hot mercury gave a better vacuum in the
lamp than cold mercury. I thereupon started to heat it. Soon all the men
got salivated, and things looked serious; but I found that in the mirror
factories, where mercury was used extensively, the French Government
made the giving of iodide of potassium compulsory to prevent salivation.
I carried out this idea, and made every man take a dose every day, but
there was great opposition, and hot mercury was finally abandoned."

It will have been gathered that Edison has owed his special immunity
from "occupational diseases" not only to luck but to unusual powers of
endurance, and a strong physique, inherited, no doubt, from his father.
Mr. Mallory mentions a little fact that bears on this exceptional
quality of bodily powers. "I have often been surprised at Edison's
wonderful capacity for the instant visual perception of differences in
materials that were invisible to others until he would patiently point
them out. This had puzzled me for years, but one day I was unexpectedly
let into part of the secret. For some little time past Mr. Edison had
noticed that he was bothered somewhat in reading print, and I asked him
to have an oculist give him reading-glasses. He partially promised, but
never took time to attend to it. One day he and I were in the city, and
as Mrs. Edison had spoken to me about it, and as we happened to have
an hour to spare, I persuaded him to go to an oculist with me. Using
no names, I asked the latter to examine the gentleman's eyes. He did so
very conscientiously, and it was an interesting experience, for he was
kept busy answering Mr. Edison's numerous questions. When the oculist
finishe