I will now point out to the young student the mode in which he may relieve his mind of any confusion, or possibly, if very young, any doubt, which the perusal of Dr. Meigs’s Sixth Letter may have raised in his mind.

The most prominent ideas of the Letter are, first, that the transmissible nature of puerperal fever appears improbable, and, secondly, that it would be very inconvenient to the writer.  Dr. Woodville, Physician to the Small-Pox and Inoculation Hospital in London, found it improbable, and exceedingly inconvenient to himself, that cow pox should prevent small-pox; but Dr. Jenner took the liberty to prove the fact, notwithstanding.

I will first call the young student’s attention to the show of negative facts (exposure without subsequent disease), of which much seems to be thought.  And I may at the same time refer him to Dr. Hodge’s Lecture, where he will find the same kind of facts and reasoning.  Let him now take up Watson’s Lectures, the good sense and spirit of which have made his book a universal favorite, and open to the chapter on Continued Fever.  He will find a paragraph containing the following sentence:  “A man might say, ’I was in the battle of Waterloo, and saw many men around me fall down and die, and it was said that they were struck down by musket-balls; but I know better than that, for I was there all the time, and so were many of my friends, and we were never hit by any musket-balls.  Musket-balls, therefore, could not have been the cause of the deaths we witnessed.’  And if, like contagion, they were not palpable to the senses, such a person might go on to affirm that no proof existed of there being any such thing as musket-balls.”  Now let the student turn back to the chapter on Hydrophobia in the same volume.  He will find that John Hunter knew a case in which, of twenty-one persons bitten, only one died of the disease.  He will find that one dog at Charenton was bitten at different times by thirty different mad dogs, and outlived it all.  Is there no such thing, then, as hydrophobia?  Would one take no especial precautions if his wife, about to become a mother, had been bitten by a rabid animal, because so many escape?  Or let him look at “Underwood on Diseases of Children,” [Philadelphia, 1842, p. 244, note.] and he will find the case of a young woman who was inoculated eight times in thirty days, at the same time attending several children with smallpox, and yet was not infected.  But seven weeks afterwards she took the disease and died.

It would seem as if the force of this argument could hardly fail to be seen, if it were granted that every one of these series of cases were so reported as to prove that there could have been no transfer of disease.  There is not one of them so reported, in the Lecture or the Letter, as to prove that the disease may not have been carried by the practitioner.  I strongly suspect that it was so carried in some of these cases, but from the character of the very imperfect evidence the question can never be settled without further disclosures.