_I._ The most important are _contractibility_ and _sensibility_. _E._ Let me advertise you that I am particularly hostile to technical words--all because I do not understand them, I allow, but please humor this ignorance by avoiding them. _I._ And thus perpetuate your ignorance, my dear Ellinora? No; this will not do; for my chief object in these conversations is that you may be prepared to profit by lectures, essays and conversation hereafter. You will often be thrown into the company of those who express themselves in the easiest and most proper manner, that is, by the use of technical words and phrases. These will embarrass you, and prevent that improvement which would be derived, if these terms were understood. Interrupt me as often as you please with questions; and if we spend the remainder of the evening in compiling a physiological glossary, we may all reap advantage from the exercise. To return to the vital principles--vital is from _vita_, life--_contractibility_ and _sensibility_. The former is the property of the muscles. The muscles, you know, are what we call flesh. They are composed of fibres, which terminate in tendons. _Alice._ Please give form to my ideas of the tendons. _I._ With the muscles, they constitute the agents of all motion in us. Place your hand on the inside of your arm, and then bend your elbow. You perceive that cord, do you not? That is a tendon. You have observed them in animals, doubtless. _Ann._ I have. They are round, white, and lustrous; and these are the muscular terminations. _I._ Yes; this tendon which you perceive, is the termination of the muscles of the fore-arm, and it is inserted into the lower arm to assist in its elevation. _E._ Now we are coming to it. Please tell me how I move a finger--how I raise my hand in this manner. _I._ It is to the contractile power of the muscles that you are indebted for this power. I will read what Dr. Paley says of muscular contraction; it will make it clearer than any explanation of mine. He says, "A muscle acts only by contraction. Its force is exerted in no other way. When the exertion ceases, it relaxes itself, that is, it returns by relaxation to its former state, but without energy." _E._ Just as this India-rubber springs back after extension, for illustration.