of boys "break," or "change," because of the sudden growth
or enlargement of the larynx, and consequent increase in length of the
vocal cords, at from fourteen to sixteen years of age. No such enlargement
takes place in the larynxes of girls: therefore their voices undergo no
such sudden change.

[51] This experiment and several others in this book, are taken from
Professor Bowditch's little book called _Hints for Teachers of
Physiology_, a work which should be mastered by every teacher of
physiology in higher schools.

[52] The teacher or student who is disposed to study the subject more
thoroughly and in more detail than is possible in a class text-book, will
find all that is needed in the following excellent books, which are
readily obtained by purchase, or may be found in the public libraries of
larger towns: Dulles' _Accidents and Emergencies;_ Pilcher's _First Aid in
Illness and Injury_; Doty's _Prompt Aid to the Injured;_ and Johnston's
"Surgical Injuries and Surgical Diseases," a special article in
Roosevelt's _In Sickness and in Health_.

[53] "A tourniquet is a bandage, handkerchief, or strap of webbing, into
the middle of which a stone, a potato, a small block of wood, or any hard,
smooth body is tied. The band is tied loosely about the limb, the hard
body is held over the artery to be constricted, and a stick is inserted
beneath the band on the opposite side of the limb and used to twist the
band in such a way that the limb is tightly constricted thereby, and the
hard body thus made to compress the artery (Fig. 160).

"The entire circumference of the limb may be constricted by any sort of
elastic band or rubber tube, or any other strong elastic material passed
around the limb several times on a stretch, drawn tight and tied in a
knot. In this way, bleeding may be stopped at once from the largest
arteries. The longer and softer the tube the better. It requires no skill
and but little knowledge of anatomy to apply it efficiently." Alexander B.
Johnson, Surgeon to Roosevelt Hospital, New York City.

[54] Corrosive sublimate is probably the most powerful disinfectant known.
A solution of one part in 2000 will destroy microscopic organisms. Two
teaspoonfuls of this substance will make a solution strong enough to kill
all disease germs.

[55] The burning of sulphur produces sulphurous acid, which is an
irrespirable gas. The person who lights the sulphur must, therefore,
immediately leave the room, and after