2. Materials and Methods
A Power Lab System (AD Instruments, Australia) was used for heartbeat recordings. For human EKGs, (abbreviation after Willem Einthoven), commercially available EKG electrodes were used. They are available worldwide, for example, a set of ready-made three AgAgCl electrodes (Vitrode V, Nihonkoden Co. Ltd. Tokyo). EKG signals were transferred to a Power Lab System. Finger pulse recordings were also used with it. For crustacean model animals' EKG, permanently mounted metal electrodes were used—they were glued on the carapace. The metal electrodes, + and –, were reaching the surface of the heart through small holes made on the carapace. All subjects and...