Abstract
High skilfulness has so far been required to record the heartbeat of insect. The new method devised by the present authors made it much easier to record the heartbeat of an intact insect.
This method was based in principle on photoelectric effect: a constant beam of light was thrown on the heart of the dorsal vassel which was seen through the middorsal cuticle. The apparatus for this method consisted of a photocell, an amplifier and a pen-writing oscillograph. The changes in a reflected light associated with heartbeat were converted to changes of potential difference by means of the photocell, and were recorded as mechanocardiogram.
The action potentials associated with heartbeat could easily be recorded from an intact insect. The apparatus consisted of one pair of electrodes, an amplifier and a pen-writting oscillograph.
The action potentials were either led off from the cuticular surface of ether-anaesthetized larva by means of one pair of forceps-type electrodes or led off from the inside of ether-anaesthetized larva by means of one pair of needle-type electrodes, and were fed to the amplifier. Thus the action potentials were recorded as electrocardiogram.
Observations on the heartbeat by these two methods were made with both the last instar larvae of grubs, Xylotrupes dichotomus L., and those of the silkworm, Bombyx mori L. The mechanocardiograms or the electrocardiograms observed with these insects were compared with those reported by other investigators.
1. The shape of waves in the mechancoardiogram from the silkworm was similar to that of the cockroach, Periplaneta americana L., studied by YEAGER (1938). Each phase in a mechanocardiogram described by YEAGER could be observed with the silkworm, i.e., i) an ascending limb associated with systole, ii) a descending limb representing diastole and iii) a slight period of diastasis. A presystolic notch appeared immediately before the beginning of the next cycle.
2. In the mechanocardiogram from Xylotrupes there appeared two notches immediately before the beginning of the period of systole and of diastasis. But these notches were lacking in the electrocardiogram and the shape of its wave differed greatly from those reported by many other investigators.
3. The highest action potential associated with heartbeat was recorded by means of the needle-type electrodes from the region where the alary muscles were located.
4. The magnitude of the action potential associated with the heartbeat of larva anaesthetized by ether was 9-15μV when it was recorded from the surface of the body, and of the order of 150μV when it was recorded from inside of the body.
5. Simultaneous recordings were made from two distant points of the dorsal vessel. It was classified from these records that each peristaltic wave originated from the posterior end of the dorsal vessel and moved toward the anterior part.
6. These methods of recording the mechanocadiogram and the electrocardiogram are considered to be available for studying the effects of insecticides, electricity and other treatments on the heartbeat of insect.
