All [knowledge] comes from experience, it is true, but experience is nothing if it does not form collections of similar facts. Now, to make collectio… - Pierre Charles Alexandre Louis

Between the one who counts the facts, grouped according to their resemblance, in order to know what to believe regarding the value of therapeutic agents and him who does not count but always says "more or less frequent," there is the difference between truth and error, between something that is clear and truly scientific and something that is vague and without value—for what place is there in Science for that which is vague?

From the exposition of facts... we infer that bloodletting has had very little influence on the progress of pneumonitis, of erysipelas of the face, and of angina tonsillaris, in the cases under my observation; that its influence has not been more evident in the cases bled copiously and repeatedly, than in those bled only once and to a small amount; that, we do not at once arrest inflammations, as is too often fondly imagined; that, in cases where appears to be otherwise, it is undoubtedly owing, either to an error in diagnosis, or to the fact that the bloodletting was practised at an advanced period of the disease, when it had nearly run its course; that, it would be well, nevertheless, in inflammations of imminent hazard, pneumonitis, for instance, to try whether a first bleeding sufficient to produce syncope, from twenty-five to thirty ounces or more, would not be attended with greater success; and finally that, wherever I have been able to compare the effect of general, with that of local bleeding by leeches, the superiority of the former has appeared to me demonstrated.

Without the aid of statistics nothing like real medicine is possible.