BREATHING 407 



tects the most delicate organs and acts as a support for the 

 attachment of the muscles. The appendages, like the legs 

 and arms in man, are jointed to the central part of the 

 skeleton, and it is the action of the muscles in moving these 

 about the joints that makes movement from place to place 

 possible. 



In the skull is situated the great nerve center of the 

 animal, the brain, and from this through the vertebral 

 column passes the great nerve distributor, the spinal cord. 

 From the brain, nerves are sent to all the muscles of the 

 body, to the skin and to those organs, like the eye and 

 the ear, which transmit to the brain impressions received 

 from without the body. These nerves give the stimuli 

 which cause the muscles to thicken, or contract. In fact, 

 all the voluntary movements of animals are controlled from 

 the brain, as the movements of trains on a railroad are con- 

 trolled from the dispatcher's office. 



Breathing. All animals must have a way to breathe, 

 or energy cannot be supplied to carry on the activities of 

 the body. Different animals breathe in different ways, 

 but in the higher vertebrates and in man it is the same. 

 Breathing in man will, therefore, be taken as the type. 



Air enters the body through the nose or mouth, and 

 passes down through the windpipe into the lungs. In order 

 to keep out dust and germs, the opening of the nose is 

 supplied with a large number of hairs projecting from the 

 mucous membrane which lines the whole nasal chamber. 

 These hairs and the secretion from the membrane catch and 

 hold most of the harmful particles. 



It is most important that air should be breathed through 

 the nose and not through the mouth. Air which enters 



