Louis PCA (1835)

Recherches sur les effets de la saignée dans quelques maladies inflammatoires et sur l'action de l'émétique et des vésicatoires dans la pneumonie [Research on the effects of bloodletting in some inflammatory illnesses and on the action of emetics and blistering in pneumonia]. Paris: Librairie de l'Académie royale de médecine.
In 1835, Pierre-Charles-Alexandre Louis compared mortality rates among Parisian patients with pneumonia who had received prompt treatment with bloodletting with other patients who had been treated later in the course of their disease.

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“What was to be done in order to know whether bloodletting had any favourable influence on pneumonitis, and the extent of that influence? Evidently to ascertain whether, other things being equal, the patients who were bled on the first, second, third or fourth day of their illness, recovered more readily than those bled at a later period. In the same manner, it was necessary to estimate the influence of age, or, more generally, any other circumstance, on the appreciable effects of bloodletting.”

(Louis 1835, p 70-71; Louis 1836, p 55)




“For example, in any particular epidemic, let us suppose five hundred of the sick, taken indiscriminately, are subjected to one kind of treatment, and five hundred others, taken in the same manner, are treated in a different mode; if the mortality is greater among the first than among the second, must we not conclude that the treatment was less appropriate, or less efficacious in the first class than in the second? It is unavoidable; for among so large a collection, similarities of conditions will necessarily be met with, and all things being equal, the conclusion will be rigorous.”

(Louis 1835, p 75-76; Louis 1836, p 59-60)



“Let us further remark that the objection made to the numerical method, to wit, the difficulty or impossibility of forming classes of similar facts, is alike applicable to all the methods that might be substituted. It is impossible to appreciate each case with mathematical exactness, and it is precisely on this account that enumeration becomes necessary. By so doing, the errors (which are inevitable) being the same in the two groups of patients subjected to different treatments, mutually compensate each other, and they may be disregarded without materially affecting the exactness of the results.”

(Louis 1835, p 75-76; Louis 1836, p 59-60)

Translation by Alfredo Morabia


Pierre Charles Alexandre Louis (1787-1872)


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