Dependence of maximal flow rates on average gland size. A: Neonatal pig nasal turbinate. B: Adult pig nasal turbinate. C: Ferret trachea. D: Mouse tracheolaryngeal region. E: Pig trachea. F: Sheep trachea. G: Human trachea. Flow rates are the sustained responses to carbachol obtained by Wine and colleagues (Joo et al., 2001; Choi et al., 2007; Ianowski et al., 2007; Cho et al., 2010, 2011). Gland sizes were calculated from data in this and other studies (Choi et al., 2000; Widdicombe et al., 2001; Cho et al., 2011). Line is best least-squares linear regression.