Those who feel a difficulty in relinquishing old opinions and adopting new views upon any particular subject, may perhaps ask how it has happened, if inflammation of the brain from protracted suckling be so common as the preceding observations and cases would appear to prove, that medical men of more advanced age and far greater experience than myself have not previously noticed the circumstance. I would observe, in reply, that until Harvey pointed out the circulation of the blood, no one ever suspected the existence of such a phenomenon; yet now the wonder appears to be, not that Harvey made the discovery, but that others had not previously done the same. Multitudes, it may be added, and among them the great Newton, had witnessed the fall of objects to the ground without thinking of the cause which produced their downward tendency; the propitious moment, however, arrived--the apple fell, and the philosopher was led to those deductions which have rendered his name immortal. So is it with observers of every class, from those most distinguished by intellectual superiority and its successful application, down to the humble writer of the present observations. Facts are continually passing before us unnoticed, till, from their repeated coincidence, or some accidental impulse, we attempt, and finally are enabled, to trace their origin. Thus, until the possibility of Meningitis originating from protracted lactation had been suggested, practitioners were, of course, unable to notice the fact--not from its non-occurrence, but because their unconsciousness of its existence must necessarily preclude the inquiries from which alone its cause could be determined. Hence a practitioner may have treated many hundred cases of water on the brain in children, without being able to attribute any one of them to protracted suckling; yet this is no proof that such cases did not happen, for, had he made the requisite inquiries, very probably many among them might have been found which had thus arisen. Another objection that may possibly be made to my views, is, that instances might be adduced where lactation had been persevered in for a very long period, without any ill effects supervening. That such frequently occur, there is no doubt; and with respect to them, I have merely to observe, that they do not in the slightest degree invalidate the correctness of my conclusions. As well might it be argued, that because persons have fallen from a very great height without sustaining any injury, or, because poisonous doses of various drugs have sometimes been swallowed without death supervening, that, therefore, there is no danger in jumping from a precipice, or in taking a virulent poison; or that death never occurs from these causes. Such cases, unless far more numerous than I imagine them, can only be regarded as exceptions to the general rule; and, consequently, do not lessen its authority, there being no rule without an exception.