INTRODUCTION 23 



As it docs not call for much imagination to think of a 

 ship or a locomotive as an integrated being, it should be 

 still easier to recognize this essential fact in the world of 

 living things. Someone has said that in the case of an 

 animal "the whole is greater than the sum of its parts" 

 and this is true in almost the same sense that a number 

 made by combining three or four figures is greater than 

 the sum of these digits. The interaction of parts makes 

 possible results which could not be attained by the parts 

 while isolated. 



The Means of Coordination. When one tries to 

 decide how the evident condition of coordination or inte- 

 gration is secured, one is likely to think first of the nerv- 

 ous system as serving just this purpose. This is a correct 

 idea, provided only that one does not fail to reserve a 

 place for other agencies. When rapid changes in a cer- 

 tain region promptly follow changes somewhere else it 

 can usually be inferred that the connecting link has been 

 a nervous one. When, for example, a blow has fallen 

 upon the head and the arm is thrown up to ward off an- 

 other, the case is one of coordination through the medium 

 of the nervous system. But the more gradual modifying 

 of the activities of one organ in consequence of those of 

 another has often a different basis. It may be due to the 

 passage of chemical products from the place of their ori- 

 gin to some other locality where they can exert an influ- 

 ence. The importance of the chemical factors in the 

 regulation of organic processes is more appreciated to-day 

 than ever before and it is likely to have a still larger recog- 

 nition in the future. 



An illustration may be given. In the normal course of 

 digestion the pancreas is found to enter upon the task 

 of secreting its valuable juice at about the time when the 

 stomach begins to transfer its contents to the small in- 

 testine. This is just when the pancreatic secretion is 

 needed and the timeliness of the action makes us curious 

 to know how it is brought about. The communication 

 between the stomach and the pancreas has been found 



