Abstract: A device for controllably delivering a solid, paste or liquid material in biological, environmental or industrial systems. The device is in the form of a tubular body, one end of which is open to allow egress of the material, and the other is closed. A gas-tight plunger slides within the body by virtue of spring driving means and gas from the external environment which enters the closed end of the tubular body by way of a gas permeable membrane and acts, together with the spring on the rear face of the plunger. The plunger controllably ejects the material from the open end of the device. The device has particular use in the delivery of therapeutic and/or prophylatic materials to animals.