A method of treating human or animal tissue, the method comprising the step of: i. directing a stream of an aqueous liquid comprising gas bubbles excited by acoustic energy towards a wound or anatomical pocket in human or animal tissue, or towards an anatomical space or potential space in human or animal tissue, or towards soft or hard tissue in an oral cavity or elsewhere in the human or animal body, or towards tissue in a nasal cavity, or towards tissue associated with sinuses, eye, ear, digestive and genito-urinary systems, thereby to treat the human or animal tissue with the stream. The output stream can clean a wound in human or animal tissue, and can treat the wound by healing the wound, for example by stimulating fibroblasts in the wound tissue and causing, promoting or enhancing re-epithelialisation of epidermal tissue in the wound.
