288 



BIOLOGY AND HUMAN LIFE 



ligaments, and ( 2 ) prolonged inaction that may permit bruised 

 tissues to grow together in an undesirable position. 



229. The muscles. The unstriped muscles are controlled 

 automatically by changes in the chemical condition in various 

 parts of the body. The striped muscles, which make up about 

 40 per cent of the body weight, are controlled by nerves of both 

 the central cerebrospinal system and the autonomic system. 



Fig. 142. The importance of suitable diet 



The child in these pictures was suffering from defective nutrition. In the first pic- 

 ture it weighed 14 pounds 4 ounces. The second picture was taken eleven weeks 

 later, after expert treatment, when the child weighed 17 pounds 15 ounces. (Photo- 

 graphs by Dr. Henry Dwight Chapin, at the Speedwell Society) 



Thus it comes about that, while these muscles are voluntary in 

 a true enough sense, they also contract and bring about move- 

 ments which we do not always intend to perform. In breathing, 

 for example, we can hold the breath for a few minutes or in- 

 crease the rate of breathing; but we cannot hold the breath 

 indefinitely, and we cannot help panting after running, and we 

 cannot help coughing under certain conditions, even though we 

 think we can make a good imitation of a cough when we wish 

 to. While most of us can make our faces produce fair imitations 



