Clinically, croup (laryngo tracheo broncho bronchiolitis) has often been thought of as either "spasmodic" or "viral" in origin. In truth, there is often overlap, with a mild viral illness setting up the airway for eosinophilis action. This occurs in the larynx and trachea in croup, the bronchi in asthma. Again, we see considerable overlap clinically, hence the child with a croupy cough and stridor who improves with Ventolin and Atrovent, due to a bronchial component. Sometimes wheeze, being the more musical of the two sounds, is less easily heard than the stridor.