1. Crackles and wheezes;Forgacs, P.;Lancet,1967
2. Fig 13 We simulated crackles by this model experiment. A syringe (1) and a microphone (Sony, ECM 150) (2) were positioned above an emptied bottle (3) which was used as a resonator. The quality factor of the resonator (Q) was reduced to about 5 by covering the internal surface of the bottle with a sheet of polyurethane foam of 0 9 cm thickness (4). The resonator was excited by a weak shock wave which was generated by applying commercial paste (Arabic Yamato, dynamic viscosity: 3-4 SI) at the orifice of the syringe and moving the piston up and down slowly. The vernier caliper at the bottom indicates 5 cm