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20 and to keep it alive. But we are met by the difficulty that if we do so the muscle will soon die. Here you see at once one of the serious disadvantages at which the physiologist is placed in the prosecution of his science. The things the natural philosopher deals with are dead things. He can isolate them and interrogate them at pleasure by experiment, submitting them to all sorts of conditions and changes of circumstances, without the risk of destroying them or even of altering the property he wishes to examine. Many of the phenomena he has to investigate are of a tolerably permanent character, and the things he operates upon are, as a rule, not the seat of constant change. I admit that this is only generally true, and that there are phenomena sometimes investigated by the physicist which are almost, if not quite, as brief and evanescent as those that come under the eye of the physiologist. Still the statement is true in the main.

The things the physiologist has to investigate only work within a narrow range of conditions. Alter the blood supply, allow drying to take place, change the temperature,