tical applications, was still empirical knowledge. That dirt was fatal they had discovered; but why it was fatal few of them knew. At this point Lister came forward with a scientific principle which rendered all plain. Dirt was fatal, not as dirt, but because it contained living germs which, as Schwann was the first to prove, are the cause of putrefaction. Lister extended the generalization of Schwann from dead matter to living matter, and by this apparently simple step revolutionized the art of surgery. He changed it, in fact, from an art into a science.
"Listerism" is sometimes spoken of as if it merely consisted in the application of carbolic-acid spray; but no man of any breadth of vision will regard the subject thus. The antiseptic system had been enunciated, expounded, and illustrated, prior to the introduction of the spray. The spray is a mere offshoot of the system—elegant and effective it is true, but still a matter of detail. In company with my excellent friend Mr. John Simon, I once visited St. Bartholomew's Hospital, and became acquainted, in its wards, with the practice of the late Mr. Callender. The antiseptic system was there as stringently applied as at King's College. Immediately before his departure to America I spoke to Mr. Callender on this subject; and he then told me expressly that his aim and hope had been, not to introduce a new principle, but to simplify the methods of Lister. And yet Mr. Calender's practice is sometimes spoken of as if it were, in principle, different from that of his eminent contemporary.
It is interesting, and indeed pathetic, to observe how long a discovery of priceless value to humanity may be hidden away, or rather lie openly revealed, before the final and apparently obvious step is taken toward its practical application. In 1837 Schwann clearly established the connection between putrefaction and microscopic life; but thirty years had to elapse before Lister extended to wounds the researches of Schwann on dead flesh and animal infusions. Prior to Lister the possibility of some such extension had occurred to other minds. Penetrative men had seen that the germs which produce the putrefaction of meat might also act with fatal effect in the wards of a hospital.
Thus, for example, in a paper read before the British Medical Association at Cambridge in 1864, Mr. Spencer Wells pointed out that the experiments of Pasteur, then recent, had "all a very important bearing, upon the development of purulent infection and the whole class of diseases most fatal in hospitals and other overcrowded places." Mr. Wells did not, as far as I know, introduce any systematic mode of combating the organisms whose power he so early recognized. But, I believe, in hardly any other department of surgery has the success of the antiseptic system been more conspicuous and complete than in that particular sphere of practice in which Mr. Wells has won so great a name.