intercalated in the same circuit the flasks containing poisonous or
dangerous substances, whose inadvertent handling might cause trouble,
are placed. In removing one of these flasks the circuit is closed, and
the electric bell notifies the pharmacist of the danger attendant on
the use of the substances contained in the flask referred to, thus
guarding against the errors due to carelessness, and quite too
frequent, especially in pharmacies.--_Chronica Cientifica._

[Illustration: FIG. 2.]

* * * * *




APPARATUS FOR DETERMINING MECHANICALLY THE REACTION PERIOD OF
HEARING.


The following apparatus, constructed after the designs of Dr. Loeb,
assistant in the Physiological Institute at Wurzburg, is for the
purpose of measuring the reaction period of hearing, that is, the
period which elapses between the time when a sound wave affects the
auditory nerve and is thence transferred to the brain, then affecting
the consciousness, and the moment when the motor nerves can be thrown
into action by the will. It is, therefore, necessary to fix both
instants--when the sound is produced and when the observer has, from
its warning, received the impulse so as to press down a key. The great
advantage of this instrument over others adapted for the same end
consists in this, that the determination in its essentials is effected