*Study of the "Knee Jerk" Reflex.*—A boy is seated on a chair with the legs crossed. With a small pointer he is given a light, quick blow on the upper margin of the patella at the point of connection of the tendon. The stroke will usually be followed by a reflex movement of the foot. Does this take place independently of the mind? (The one upon whom the experiment is being performed should assume a relaxed condition and make no effort either to cause or prevent the movement.) Can the movement be inhibited (prevented)? Repeat the experiment, effort being made to prevent the movement, but not by contracting opposing muscles. Other reflex actions adapted to class study are those of the eyes, such as the closing of the lids on moving objects near them and the dilating of the pupils when the eyes are shaded. The involuntary jerking of the head on bringing the prongs of a vibrating tuning fork in contact with the end of the nose is also a reflex action which can be studied to advantage. *To determine the Reaction Time.*—Have several pupils join hands, facing outwards, making a complete circle, excepting one gap. Give a signal by touching the hand of one pupil at the end of the line. Let this pupil communicate the signal, by pressure of the other hand, to the next pupil and so on around, having the last pupil raise the free hand at close of the experiment. Note carefully the time, preferably with a stop watch, required to complete the experiment and divide this by the number of pupils, to get the average reaction time. The experiment may be repeated with boys only and then with girls, comparing their average reaction time. *Reflex Action of the Salivary Glands.*—Place a small pinch of salt upon the tongue and note the flow of saliva into the mouth. Try other substances, as starch, bits of wood, and sugar. What appears to be the natural stimulus for these glands? Compare with reflex actions of the muscles. CHAPTER XIX - HYGIENE OF THE NERVOUS SYSTEM The far-reaching effects and serious nature of disorders of the nervous system are sufficient reasons for considering carefully those conditions that make or mar its efficiency. Controlling all the activities of the body and affecting through its own condition the welfare of all the organs, the hygiene of the nervous system is, in a large measure, the hygiene of the entire body. Moreover, it is known that some of our worst diseases, including paralysis and insanity, are disorders of the nervous system and are prevented in many instances by a proper mode of living.