THE NERVOUS SYSTEM 315 



the diaphragm (di'd-fram) divides the body cavity into two unequal 

 cavities. In the upper one, thoracic cavity, are found the heart, 

 lungs, and esophagus; in the lower, the abdominal cavity, are the 

 stomach, intestines, the liver, the kidneys, and other structures. 



Digestion and excretion. The mouth cavity leads into a food 

 tube into which food passes and from which digested or liquid 

 food is absorbed into the blood to be carried to the cells of the 

 various organs which do the work. Emptying into this food tube 

 are various groups of gland cells, which pour digestive fluids over 

 the solid foods, thus aiding in changing them to a soluble form. 

 Solid waste materials are passed out through the posterior end of 

 the food tube, while liquid wastes are eventually excreted by means 

 of the skin and of organs called kidneys. 



The nervous system. This complex machine is much more 

 than a mechanical engine. It is self-directed. All its functions 

 are either directly or indirectly under its control. Not only are 

 animals able to receive outside stimuli through certain parts called 

 sense organs, but they react to them, and there is internal co- 

 ordination and control as well. The complicated machine does 

 its work automatically; the heart beats, the glands secrete, the 

 chest rises and falls without any conscious direction on our part. 

 The nervous system gives sensation, it gives internal control and 

 coordination. In man it does more. It also gives him control 

 over his conscious activities. He is able to make a selection or 

 choice of his daily acts. As such he is a " thinking " animal and 

 has become master of the earth. 



Practical Exercise 1. Make in tabular form for your workbook a summary 

 of work done by the different parts of the body. 



Self-Testing Exekcise 



Check in your workbook the statements that are true. 



T. F. 1. The human body is like a machine because it can repair 

 itself. 



T. F. " 2. Food is oxidized in the human body as is fuel in an engine. 



T. F. 3. The skin is an organ of protection but not of excretion. 



T. F. 4. The nervous system gives sensation as well as body control. 



T. F. 5. Movement is accomplished in the body because muscles 

 are attached to bones which act as levers. 



