This decline occurred even though many medical theories were brought to the defense of bleeding. A French medical observer commented in 1851 that "l'histoire de la saignee consideree dans son ensemble, constituerait presque a elle seule l'histoire de toutes les doctrines medicales" (the history of bloodletting, considered in its totality, would constitute almost by itself the history of all medical doctrines).[72] There was no crisis of medical opinion, and no one event to account for this decline. The French physician, Pierre Louis's statistical investigation (numerical method) into the effect of bloodletting in the treatment of pneumonia has often been cited as a cause for the downfall of venesection,[73] but the results of Louis's research showed only that bloodletting was not as useful as was previously thought. Louis's work, however, was typical of a new and critical attitude in the nineteenth century towards all traditional remedies. A number of investigators in France, Austria, England, and America did clinical studies comparing the recovery rates of those who were bled and those who were not.[74] Other physicians attempted to measure, by new instruments and techniques, the physiological affects of loss of blood. Once pathological anatomy had associated disease entities with specific lesions, physicians sought to discover exactly how remedies such as bloodletting would affect these lesions. In the case of pneumonia, for example, those who defined the disease as "an exudation into the vessels and tissues of the lungs" could not see how bloodletting could remove the coagulation. John Hughes Bennett, an Edinburgh physician, wrote in 1855: "It is doubtful whether a large bleeding from the arm can operate upon the stagnant blood in the pulmonary capillaries--that it can directly affect the coagulated exudation is impossible."[75] Bennett felt that bloodletting merely reduced the strength of the patient and thus impeded recovery. Bloodletting was attacked not only by medical investigators, but much more vehemently by members of such medical sects as the homeopaths and botanics who sought to replace the harsh remedies of the regular physicians by their own milder systems of therapeutics.[76] As a result of all this criticism the indications for bleeding were gradually narrowed, until at the present time bloodletting is used in only a few very specific important instances.