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HlSTUin' OF DENTAL SURGERY 307

(3) That to control plT^^pllrc• it imist l)e ])ositivc witli alternating periods
of movement and rest.
(4) That these conditions can only he met by the use of the screw in some
of its many forms, and occasionally by tJie inclined plane, because in each of
Ihese cases the ])ressure is intermittent.
After a long series of experiments upon the natural leetli l)r. Farrar ar-
rived at a c(melusion in regard to permissible movement in regulating which
he fornjulated into the following "law."
In regulating teeth the dividing line between the production of physiological and
pathological changes in the tissue of the jaw is found to lie within a movement of the
teeth acted upon—allowing a variation which will cover all cases—not exceeding 1/-40 or
1/160 of an inch every twelve hours.
His views upon these jioints were never endorsed by other writers nor
aceejited by the profession. His various articles show that while he did place
has greatest reliance upon the j)rinciple of the screw, in his practice he also
frequently resorted to the use of elastic rubber, springs, ligatures and vulcanite
plates. He devised many ap])liances for producing individual movement of
teeth, all of which were constructed of precious metal, principally gold. Later
iliese were made by the S. S. A\niite Company, and ottered for sale in the lielief
that practitioners would gladly avail themselves of them, but tliev did not meet
with favor and were soon withdrawn from the market.
In 1888, Dr. Farrar published the first volume of his monumental work,
entitled "Irregularities of the Teeth and their Correction." In 1898 the sec-
ond volume ajipeaied. 1'hesc volumes contained not only the results of his
earlier work as ]iublished in dental periodicals, but a large mass of new matter
covering his later experience, as. well as a valuable historical outline of the
work of his predecessors. With all tlie wealth of information imparted in re-
gard to the methods of moving teeth to tiring them into the arch line, the
author seemed not to have realized the necessity of bringing about a new
arrangement of one or both dental arches so that normal occlusion would re-
sult—a matter of the greatest importance. His various devices and appli-
ances as explained and ilhtstrated evidence an intimate acquaintance with
mechanical principles and great ingenuity, but their complicated character evi-
dently prevented their general adoption.
At the seventh International Medical Congress, held in London in 1881,
\¥.\LTER H. Coffin read a paper on "A Generalized Treatment of Irregulari-
ties" in which he described his own and his father's method of treating cases