This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1885. Not illustrated. Excerpt: ... have slain, and the panic they spread around them, the danger which a person affected with one of them becomes to his fellowcreatures, and the broken constitutions and disfigurements they so often leave behind even when they spare life, we can form an idea of the immense and incalculable blessing which their extinction would be to mankind. The great fact which warrants us in believing that these diseases might be entirely extirpated, or "stamped out," is, that whatever their primary origin in past ages may have been, they never iiow-a-days arise spontaneously, but are invariably propagated by infection. They are not merely infectious diseases, but have no other source than infection. "They are communicated from person to person by contagion," says Sir Thomas Watson, "and, as I venture to maintain, arise in no other way; and this quality, with their non-recurrence, forms the key to their supreme interest." Small-pox, for example, never arises except by contagion from a pre-existing case of small-pox. measles from a pre-existing case of measles, scarlet fever from scarlet fever, and so on with the rest. Moreover, they always, to use a common expression, "breed true," propagating their own kind, and no other, and maintaining their characteristic type and features unchanged from generation to generation. Thus measles always breeds measles, and never scarlet fever or hooping-cough; typhus breeds typhus, and never typhoid fever; and each disease runs the same course in the present day, has the same average duration, and presents the same symptoms as it did when first clearly described by the earlier physicians. In the above respects the infectious fevers bear a close and most striking resemblance to the different species of plants and animals. We do not know how these...