Techniques have been developed for casting both solid and hollow lung models from lung specimens. These techniques have been used to make casts of rat, rabbit, baboon, and human lungs and may be used for other species. An air line at a positive pressure of 25 cm of water is connected to the trachea to air-dry lungs that have been surgically removed from the species. To make a solid model, silicone rubber is injected in to the dry lung. Solid models also can be made by injecting silicone rubber directly in situ using saline displacement techniques. Nasopharynx casts are made by direct injection of silicone rubber through the trachea. Using the lost wax technique, a hollow cast of the airways and the nasopharynx can be made. Anatomical differences in lungs and nasal passages have been observed among species. Current research investigates casting of the respiratory tract starting at the nares and extending through the larynx to the tracheobronchial tree.