_The variety of response to the demand for study_

After we have become acutely conscious of a misfit somewhere in our
experience, the actual study done to right it varies indefinitely with
the individual. The savage follows a hit-and-miss method of
investigation, and really makes his advances by happy guesses rather
than by close application. Charles Lamb's _Dissertation on Roast
Pig_ furnishes a typical example of such accidents.

The average civilized man of the present does only a little better.
How seldom, for instance, is the diet prescribed for a dyspeptic--whether
by himself or by a physician--the result of any intelligent study!
The true scientist, however, goes at his task in a careful and systematic
way. Recall, for instance, how the cause of yellow fever has been
discovered. For years people had attributed the disease to invisible
particles which they called "fomites." These were supposed to be given
off by the sick, and spread by means of their clothing and other
articles used by them. Investigation caused this theory to be abandoned.
Then, since Dr. J. C. Nott of Mobile had suggested, in 1848, that the
fever might be carried by the mosquito, and Dr. C. J. Finlay of
Havana had declared, in 1881, that a mosquito of a certain kind would
carry the fever from one patient to another, this variety of mosquito
was assumed by Dr. Walter Reed, in 1900, to be the source of the
disease, and was subjected to very close investigation by him. Several
men voluntarily received its bite and contracted the fever. Soon,
enough cases were collected to establish the probable correctness of
the assumption. The remedy suggested--the utter destruction of this
particular kind of mosquito, including its eggs and larvae--was so
efficacious in combating the disease in Havana in 1901, and in New