In Chapter 13 entitled "Applications", it states the following regarding Eucalyptus globulus:  "The aim of the bronchitis treatment is to loosen mucus in the bronchial passages and to stimulate its elimination with mucolytic essential oils.  This should be followed up with expectorant oils (Eucalyptus radiata and Eucalyptus globulus are also effective against the viruses causing bronchitis).  Oils can be applied to the chest, over the whole body, or be inhaled."...."Effectiveness:  aromatherapy treatments for a fully developed bronchitis offers no miracle cures, but it stimulates sustained improvement by preventing bacterial secondary infections. (Most cases of bronchitis are caused by viruses.)"  

Reference:  Kurt Schnaublet, Ph.D., in the book entitled "Medical Aromatherapy, Healing with Essential Oils", North Atlantic Books, Berkeley, California, 1999, pages 229-230.