15* 



HUMAN BIOLOGY 



A = Correct posture. 



B = Incorrect posture. 



is largely a matter of muscular train* 

 ing. In standing (Fig. 48) , the head 

 and body should be erect, the heels 

 brought close together, and the 

 shoulders brought into such a posi- 

 tion that the back is approximately 

 flat . In sitting (Fig. 49) , care should 

 be taken not to bend the body over 

 the desk, and a proper relation 

 between height of chair and desk 

 should be secured. 



Permanent curvature of the spine 

 frequently results from carrying 

 loads of books or other heavy ob- 

 jects on one side of the body only; 

 pupils should therefore train them- 

 selves to use the arms alternately 

 for this purpose. 



IV. THE NERVOUS SYSTEM 



228. The body as a collection of 

 organs. In the preceding chap- 

 ters we have discussed the diges- 

 tive, respiratory, and circulatory 

 systems and have seen that these 

 organs furnish all parts of the body 

 with food and oxygen. We have 

 studied the process of oxidation 

 whereby we keep warm and gain 

 the power to do work. And finally 

 we are familiar with the fact that 

 the bones and muscles are the 

 organs that give support to the 

 body and provide the machinery 



for all our motions. Thus we see that the body is composed of 

 many organs, each with its special function or functions. 



C = Desk and seat too low. 

 FIG. 49. Sitting positions. 



