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neither agreement nor argument, because the one had mentally imposed a restrictive sense upon the terms employed, which was not recognised by the other.
The importance of this subject will be noted hereafter; it has been mentioned here merely as an illustration of the need of clear definitions. But I think we may draw other useful lessons from the controversy which has occupied so large a portion of the days of living physiologists. It had been formulated as a law, that putrefaction and the development of living organisms bore some constant relation to each other. Its exact bearing had not been reached, but its application seemed to be universal. Here let me just observe the difference between a "law" and a "cause." The law merely declares the certainty with which the cause acts. The law does not compel obedience; it merely shows how the result is to be traced, as the effect of some definite, though perhaps unknown, influence. In the case before us, the law was a very imperfect one, the cause utterly unknown. It had been suggested that, somehow or other, the presence of atmospheric air was essential, and experiments were being made to ascertain which of its constituents originated the change. Tyndall's experiment seemed to point to some ingredient mechanically suspended in the air; other observations tended in the same direction,
