Page:The Harveian oration 1866.djvu/28

 quarter, by an old man from a youth, by a person of understanding from one of inferior capacity" (q).

Is there nothing more that we may learn from Jenner's discovery? Is there nothing it may suggest?

The protective power of Vaccination appears at present as an isolated fact. An isolated fact in Science (r). But is it an isolated fact in Nature? Is it probable that there is but a single instance in Nature of one disease so modifying a man's constitution, as to render him less liable to another disease? Or—to extend the question—is there no manageable agency, derivable from animal life or any other source, by which such a modification might be effected? How are we to explain the familiar fact that some individuals escape a fever, when others, perhaps less exposed, catch the infection? A greater liability may be attributable to a low, ill-defined condition of the general health:

But the immunity from such attacks is plainly not