^S?gX 



CHAPTER 12 

 THE ENDOCRINAL ORGANS 



One problem of a living organism is to get its organs to work together. 

 In fact, the difference between a living creature and a dead one is that 

 the living organism is integrated and the dead is not. Moreover, the 

 more complex an organism, the more difficult it is to secure functional 

 correlation among its different but interdependent parts, and the more 

 complicated is the mechanism which accomplishes this end. 



PITUITARY 



-PARATHYROIDS 



, — ^r^l THYMUS 



PANCREATIC 

 I SLANDS 



GONAD -■— V 



Fig. 373. — The endocrinal glands in man. 



This functional integration of the animal body is brought about by 

 two means, one nervous, the other chemical. In general, quick adjust- 

 ments, muscular activities and correlations, and responses to the outward 

 environment are controlled by the nervous system. But growth, for 

 example, metabolism, and in general the adjustment of the several tissues 

 to one another, is largely taken care of by the ductless or endocrine glands, 

 which secrete into the blood stream minute quantities of so-called hor- 

 mones that speed up ordinary chemical reactions. With the discovery 



446 



