Terahertz (THz) irradiation of excised Eisenia andrei earthworms is shown to cause overriding of the genetically determined, endogenously mediated segment renewing capacity of the model animal. Single-cycle THz pulses of 5 µJ energy, 0.30 THz mean frequency, 293 kV/cm peak electric field, and 1 kHz repetition rate stimulated the cell proliferation (indicated by the high number of mitotic cells) and both histogenesis and organogenesis, producing a significantly higher number of regenerated segments. The most conspicuous alteration in THz-treated animals was the more intense development of the new central nervous system and blood vessels. These results clearly demonstrate that THz pulses are capable to efficiently trigger biological processes and suggest potential applications in medicine.

The transmission of THz, near-infrared (1030 nm), and green (515 nm) pulses through Eisenia andrei body wall is studied, which consists of epithelial layer and circular and longitudinal muscles. Samples with the full-body cross-section were also investigated. The transmitted power for the green pulses followed the Beer-Lambert law of exponential attenuation for all thicknesses and tissue structures. Different body wall and body center absorption coefficients were found in case of infrared pulses. In the THz range, the body wall absorption coefficient steadily increases from about 80 cm–1 at 0.2 THz to about 273 cm–1 at 2.5 THz. Numerical estimation indicates that THz pulses of 5-μJ energy and 1-kHz repetition rate (5-mW average power) cause only a small temperature increase of about 0.4 K, suggesting that heating has minor contribution to biological effectiveness.

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