156 REPORT — 1855. 



calculations of chances, very often amounting to that of the instantia crucis, but 

 which is frequently misunderstood. 



The principles thus acquired, by the mere force of numbers, as to the external 

 causes of diseases, involving the knowledge of the means of preventing them, in the 

 last half-century, he considers to be of such practical importance as to bear a com- 

 parison with the knowledge acquired during that time in any other department of 

 science ; but unless this last peculiarity, of the amount of negative observation 

 which supports the positive observation, is duly considered, the strength of the 

 evidence is often most unfortunately underrated. 



The most extraordinary example of such observations, strictly empirical, esta- 

 blishing a principle as to the external cause of a disease of extreme malignity, which 

 is adequate to its extirpation from the face of the earth, is in the case of Vaccina- 

 tion. No information that we possess of the nature or mode of action of the virus 

 of small-pox, could have led us even to conjecture that it would undergo the change 

 that is now ascertained, simply by observations statistically arranged, result from 

 its passage through the body of the cow, i. e. that, if subsequently applied, in a 

 quantity almost infinitesimally small, to the human body, it would excite a local 

 specific inflammatory process, devoid of danger, and incapable of communication 

 through the medium of the air ; and that this process once undergone should not 

 only protect the living animal matter in which it is excited against any action of the 

 virus in future, but should act prospectively on the matter, which may constitute 

 the body of the same person after 60, 70, or 80 years,— either totally preventing all 

 effect of the virus, or, if an effect is produced even at that distant period, so far 

 modifying it as to render it almost absolutely innocuous at a period when we know 

 that the living structure has been repeatedly worn down and built up again, and can 

 no more be said to be the same as went through the process of vaccination in infancy, 

 than, according to the ancient paradox, a man can be said to have used the same 

 water twice who has bathed twice at the same spot and in the same river. 



It is, in like manner, by simply empirical observation, i. e. by Statistics, that we 

 have acquired within these few years information touching the extension of another 

 epidemic, sometimes attended with peculiar interest and fatality, the puerperal 

 fever, which enables us almost with absolute certainty to predict that its propaga- 

 tion after the manner of an epidemic may hereafter always be prevented ; the 

 observations of Dr. Semmelweiss, at the great Lying-in Hospital at Vienna, where 

 6000 births take place in a year, and where the deaths in child-bed were reduced to 

 the extent of 400 in the first year, that the precautions founded on these observa- 

 tions were enforced (coinciding in their import with many others, both on a large 

 and small scale, made in this country), having been, as the author maintains, sufB- 

 cient to prove, — 1 . That this disease is essentially a case of the diffuse or erythe- 

 matic inflammation, originating in the uterus, and probably passing through the 

 Fallopian tubes, to affect the peritoneal surfaces, and, like other cases of diffuse 

 inflammation (when prevailing epidemically), varying remarkably in the nature of 

 the accompanying fever, and the practice most effectual in different epidemics. 2. 

 That the immediate exciting cause of this epidemic inflammation in puerperal cases, 

 is a virus identical with that which has been termed the Cadaveric poison, often 

 evolved during the decomposition of the human body, but chiefly in the early stage 

 of that process ; and that it is transmitted from one patient to another by accou- 

 cheurs or nurses, themselves in good health, but to whose persons or clothes it has 

 become attached ; and may be prevented from extending in this way simply by pre- 

 venting all persons who may have been thus brought in contact with it, from having 

 any intercourse with patients in child-bed until effectually purified. 



The facts ascertained as to epidemic yellow fever, and its origin in malaria in hot 

 climates, and limitation to districts nearly on the level of the sea — particularly by 

 Reports to the Governments in Germany and France, bearing the names of Hum- 

 boldt and Dupuytren— and those ascertained as to the different kinds of diet which 

 can produce scurvy, and as to the efficacy of acid fruits in preventing it ; and like- 

 wise as to the power of cod-liver oil, if not of other animal oils, over the tendency 

 to scrofula, he stated also as principles in Etiology of extreme importance, founded 

 simply on Statistics. 



On the subject of the propagation of Cholera, the author coincided with the 



