Apparatus for Stimulation of Insect Sense-Organs by Air Puffs

DURING work on the relation of acetylcholine to nervous activity in insects 1,2 an apparatus was devised for the stimulation of the sensillæ of the cerci of Periplaneta americana L. by puffs of air. Since the apparatus allows separate control of strength, duration and frequency of the puffs of air, it is felt that it might find applications in other problems. The apparatus consists of an electronic switch controlling a solenoid valve through which compressed air is led to the point of application. A pressure regulator in the air line determines the strength of the puffs of air, while the duration and frequency are determined by the electronic switch. The operation of the electronic switch (Fig. 1) is as follows. Firing of the thyratron V 2 causes a surge of current through the relay L , depressing the three contacts. This activates the solenoid valve, charges condenser C 2 , cuts out V 2 and allows C 5 (or C 4 or C 6 , according to the setting of S 2 to discharge through L . The relay armature remains in this position for a period determined by the LC 5 time-constant and then returns to its normal or upper position, closing the solenoid valve, recharging C 5 and reconnecting V 2 . The voltage on C 2 now leaks off through R 3 , R 4 , P and L , producing a slowly decaying bias on V 2 (which may be altered by the setting on P ) until V 2 again fires, repeating the cycle. Thus the setting on P determines the time during which the solenoid valve is closed, while the capacity of the condenser selected by S 2 determines how long it is open. The potentiometer P provides intervals from 0.45–8.0 sec., the calibrated scale being slightly expanded in the lower range, while with S 2 times of 0.13, 0.25 and 0.56 sec. were obtained. Other time-intervals are possible by altering the capacity of condensers C 2 to C 6 .