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in the knowledge of these organisms which are placed at the very threshold of animal life, but capable it would seem of stopping the course of life itself in the highest forms of development.
It would be premature to say that the morbific germs of ague and of fever have been fully recognized, but it would be an incalculable boon if the germs of such diseases as cholera, of scarlet fever, of small pox could be so made out, that we might be led to measures which would mitigate their severity, render them harmless, and stop the ravages which they produce. In reference to the last named, small pox, if one fact more than another in medical science seems to be established it is, that by vaccination properly performed the system becomes so fortified against variola that the severity of the disease is mitigated, and that it is frequently rendered almost harmless in its attack or entirely warded off.
It may be quite correct that, in some cases after vaccination from syphilitic subjects the system may become contami-
