Page:The Harveian oration 1866.djvu/53

 infection from the various fevers! Instances are familiar to every medical practitioner, in which a person apparently in good health catches a fever, to which, on a prior occasion, he had been exposed with impunity. A wife, who has nursed her husband through scarlet fever without suffering from the infection, takes it some years afterwards while nursing her daughter. A medical practitioner, who all his life had been attending cases of fever with impunity, catches it in his old age.

Again, with respect to the protective power of Vaccination, and why it is perfect in some persons, imperfect in others? Are all the latter cases to be explained by want of care in vaccinating, or lapse of time since the operation? May not the liability be due in some cases to a fresh modification of the constitution, ex. gr. by some disease subsequent to the vaccination?

At Swavesey, a populous village in Cambridgeshire, typhoid fever was very prevalent and severe in the year 1850. In 1865, on the occurrence of a few cases of small-pox, the inhabitants in alarm, young and old alike, sought for vaccination. Accordingly, Mr Daniell, the resident surgeon, vaccinated 616, many of whom had been vaccinated on a former occasion, or had had small-pox. Of course in a large proportion of these Mr Daniell's vaccination was unsuccessful, but by no means in all such. Mr Daniell noticed the remarkable fact, that the cases of successful vaccination, in those who had been already vaccinated or had had small-pox, were chiefly, or almost wholly, among persons who had had the typhoid fever in 1850.