effected, that the heart pumps the blood, and that the lungs are used for breathing. We can stop the machine and study the form and structure of the various parts. This is the province of the anatomist. Further, as I have said, we can watch the machine in action. This is the work of the physiologist. But the peculiarity of the physiologist's machine is that each part of the mechanism is alive. Each individual organ is a machine or instrument by itself, and its use as a part of the whole complex machine depends on the molecular machinery which composes the individual organ. Returning to the analogy of the watch, it is as if each wheel, and pinion, and chain were a separate machine, more complex, perhaps, in structure than the watch itself. It is as if we had wheels within wheels, and as if the mechanism depended partly on the large wheels, and partly and mainly on the small wheels within the large ones.
In like manner our study of muscle must include the action of the muscle as a part of the body, and also the changes that happen in the muscle itself, and by which it works. We shall take the last part of the investigation
