assume that the fish means to get caught, any more than the moth intends 

 to get singed in a flame. Neidier can avoid acting as it does. 



Human Automata Winking, sneezing, coughing, swallowing and 

 other familiar reflexes take place in the human organism in direct response 

 to some stimulus. They are acts that take place without being intended or 

 desired. They take place in practically the same way in all members of the 

 species, and, generally speaking, they cannot be prevented. Human beings, 

 like other living things, sometimes act like mechanisms. 



A different type of automatic response that is at the same time adaptive^ 

 or helpful in keeping the organism going, we have already considered in 

 connection with homeostasis (see page 194), When you increase your mus- 

 cular work for any purpose — moving furniture about, climbing stairs — your 

 heart begins to speed up, your breathing changes, your kidneys begin to 

 work faster. Some of these alterations are more like plant responses, result- 

 ing from chemical and physical interactions. Speeding up the respiration 

 rate, however, is a reflex: this is set up by a chemical stimulation (in- 

 creased concentration of carbon dioxide in the blood) upon a certain nerve 

 center. 



Our reflexes do not always show themselves in movements. When the 

 "funny bone" is struck, for example, we become aware of a tingling sensa- 

 tion in the palm of the hand. This is apparently due to the reflex con- 

 traction of small skin muscles, which in turn stimulate sensory nerves. 

 "Watering of the mouth" is a gland reflex to an odor stimulus. 



Reflexes and Tropisms Reflex action differs from the tropic move- 

 ments of plants in being usually much more rapid, and in resulting from a 

 different kind of structure, or mechanism. Reflexes depend upon nerve cells 

 and nerve connections, and the movements themselves involve muscles — 

 two kinds of cells that we do not find in plants. 



To say that a reflex act is like the movement of a bell clapper when the 

 right button is pushed may seem to belittle human conduct; nevertheless the 

 statement appears to be true. However, we must not read it to mean that 

 human action is "nothing but mechanical", for each reflex is but a fraction 

 of human behavior, and there is much more that cannot be described or 

 "explained" as mechanical. 



Instincts When a baby is touched on the cheek near the mouth, he 

 turns his head to bring his mouth toward the point of contact. When an 

 object touches his lips, the baby usually opens his mouth and grasps the 

 object. When something gets into the mouth, the touch stimulus sets up 

 the sucking movements. When something touches the back of the throat, 

 the stimulus starts the swallowing reflex. Here is a chain of reflexes which 

 together bring about adaptive action. We can show that each step is a reflex 

 by setting it off independently of the others. 



264 



