"In any epidemic... let us suppose five hundred of the sick, taken indiscriminately, to be subjected to one kind of treatment, and five hundred others, taken in the same manner, to be 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 condition will necessarily be met with, and all things being equal, except the treatment, the conclusion will be rigorous."

“All comes from experience, it is true, but experience is nothing if it does not form collections of similar facts. Now, to make collections is to count.”

“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; that 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, being the same in two groups of patients subjected to different treatment, mutually compensate each other, and they may be disregarded without sensibly affecting the exactness of the results.”

“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.”

“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?”