food, moves the eyes and ears, and makes sounds with the lungs and larynx. 

 These muscles are called voluntary, being under more or less direct control 

 of the central nervous system — the brain and spinal cord; or they contract 

 in response to stimuli received by the sense organs. The heart muscles, how^- 

 ever, are striped, but are not controlled voluntarily. 



The smooth muscles relate the parts of the body to one another. Their 

 contractions w^ork the stomach wall, move the food along in the diges- 

 tive tube, and control the diameters of the blood vessels. These involun- 

 tary muscles make up a system that works constantly, even while we are 

 asleep. Life may go on indefinitely if most of the skeletal muscles are 

 paralyzed, but if the smooth muscles are paralyzed, death comes quickly. 



Infantile paralysis is a communicable disease, apparently caused by a 

 virus. It is often fatal, but where victims recover they are usually crippled 

 for life. No cure has been found for this disease. However, Elizabeth 

 Kenny, an Australian nurse, found a way to prevent the paralysis in those 

 who recover. In 1910 she had four sick children on her hands in a village 

 far from hospitals and physicians, and she set to work with them, doing the 

 best she could. The children recovered and she saved them all from becom- 

 ing crippled. She had noticed that in the acute and most painful stage of the 

 disease the skeletal muscles are in a state of continuous contraction or spasm. 

 She helped the children to relax these muscles by means of hot applications. 

 Then she helped the blood circulation move through the muscles by mas- 

 saging them and by moving the limbs. Later she got the children to try to 

 move the parts themselves, until they gradually acquired control over their 

 muscles. Her method has been recognized by physicians to be sound and 

 practical; and she has been training hundreds of nurses and technicians to 

 use the method for preventing those who are attacked by the disease from 

 remaining crippled. 



Our Double Nervous System Corresponding to the two sets of mus- 

 cles, we have two sets of nerves: (1) The spinal cord and the brain, with 

 their connections with the receptors and effectors, regulate the adjustment 

 of the organism to its surroundings. (2) The autonomic, or self-regulating, 

 system connects the internal organs with one another (see illustration, 

 p. 295). It has no central organ. It consists of a double series of ganglia, 

 or nerve-cell clusters, located in front of the spinal column (see illustration, 

 p. 278). 



We have already seen that as the activities of the brain and of the mus- 

 cles vary, there is an automatic regulation of the heart, of breathing, of the 

 blood-vessels, and of various glands. Some of these adjustments seem to 

 result directly from an alteration of the processes in a remote part by chemi- 

 cal substances in the blood. When you increase muscular activity, for ex- 

 ample, oxidation in the tissues is increased, and more carbon dioxide is 



294 



