Phthisis is characterized by a 'progressive disorganization' of the lung, which may assume a tuberculous, ulcerous, calculous, granulous, melanotic, or cancerous form; and it must he con fused neither with irritation of the mucous membranes (catarrh), nor with alteration of the serous secretions (pleurisy), nor, above all, with an alteration that also attacks the lung itself, but in the form of inflammation, namely, chronic pleuropneumonia.