According to Fraenkel,1 emphysema is found in more than 5 per cent of all autopsies. It is rarely found in children, but increases in frequency with each decade. It is often present in persons about 40 years of age, and frequently occurs during old age. Generally it is described as occurring in three types (excluding interstitial emphysema, which has no relation to the disease under discussion) namely: compensatory, atrophic and hypertrophic or vesicular emphysema. TYPES OF EMPHYSEMA Compensatory. —Compensatory emphysema is a condition in which one portion of the lung increases in size and function, when another portion is destroyed or temporarily useless. It occurs, for instance, in association with pneumonias, pleural effusions and pneumothorax. Anatomically, there is found an enlargement of the normal lung; there are no variations from the normal structure; the unaffected lung, as a result of distention, has an increased vital capacity and is able to