The present invention provides improvements in the feedback and control systems employed in the field of ventilation therapy. In particular, a system for delivering a supply of gases to a patient is described which incorporates a detachable cartridge or open tubular section (22) used to house a mechanism (11) which senses the humidity, temperature, flow and other attributes of the flowing gas. Information obtained from the sensor may be used to provide feedback to a controller (9) which controls the humidification mechanism in order to provide optimally humidified gases to a patient (1). It will be appreciated that the feedback and control system as described in the preferred embodiment of the present invention can be used in respiratory care generally or with a ventilator.