Serum therapy has afforded a large field for speculation and exploration, and the achievements in it have marked an era in medicine. The brilliant success of antidiphtheritic serum have assured us of the practicability of this mode of treatment in bacterial diseases, and we are justified in the hope that like results will be obtained in many or all diseases of this character. It now remains for us to determine the bacteria which produce a given disease and provide a suitable medium for their cultivation, and the proper organisms for the production of antitoxins, and we may hope for a specific agent in the disease in question.
The task here briefly laid out is by no means an easy one. All diseases are not of bacterial origin. Again, the most virulent microbes do not always stand artificial cultivation without deterioration, and the tolerance or natural immunity in species or individual