Page:Life in Motion.djvu/102

82 hook attached to the thread. One of these muscles is fresh and the other is dead, and has been so for many hours. I shall suspend equal weights, so as to see how much each muscle will carry, and we will find that the dead muscle will tear sooner than the living one. Its cohesion is not so great. Further, we may notice that the dead muscle scarcely stretches when I put the weights on, but the living one stretches considerably, that is to say, the living muscle is extensible. Now watch the living one closely. I shall connect it with this lever, so that we may see its movements better. You observe when I put a weight on it, it stretches, and when I remove the weight it returns to almost, but not quite, its original length; that is to say, it is extensile and retractile. This property of becoming extended and then returning to its original length is still by most physiologists described under the name elasticity, but I prefer to retain this term for the property a muscle has of returning to its original length after it has contracted. If, however, we regard muscle as a passive structure, then we find that it is a slightly but perfectly elastic body. It yields to a weight,