196 THE HUMAN BODY 



innervations to any organ come to it by way of different grand 

 divisions. The cranial and sacral groups stand in opposition to 1 lie 

 thoracico-lumbar group. It does not follow that one grand divi- 

 sion is always inhibitory and the other augmentory. As a matter of 

 fact the thoracico-lumbar system augments some activities and 

 inhibits others. Whichever are augmented by the thoracico- 

 lumbar are inhibited by the cranial or sacral, and vice versa. 



Significance of Thoracico-Lumbar and Cranial-Sacral Func- 

 tions. During the ordinary life of the individual the balanced 

 action of the opposing subdivisions of the autonomic system serves 

 to carry on the normal quiet functioning of the maintenance 

 mechanisms of the Body, which, as stated previously (p. 115), are 

 Operated by smooth muscle. As we study in detail these structures 

 in later chapters we shall see how admirably through this balancing 

 of opposing innervations they are kept in just the desired degree of 

 . activity. 



In addition to this, which we may call its routine function, the 

 thoracico-lumbar system shows a special, and very significant, 

 property which can be made clear through a tabulation of a few of 

 the many bodily changes governed by the autonomic system, with 

 the respective parts played by the thoracico-lumbar and cranial- 

 sacral systems set down. 



Thoracico-lumbar Cranial-sacral 



Pupil of eye dilated contracted 



Salivary secretion inhibited excited . 



Hair erected depressed 



Blood-vessels of skin . . constricted (pallor) . . dilated (flushing) 



Heart accelerated slowed 



Digestive organs inhibited excited (to normal activity) 



If we consider an individual whose pupils are dilated, whose 

 mouth is dry, whose hair tends to stand on end, whose face is pale, 

 whose heart is racing, and whose stomach is a leaden weight within 

 him we have no difficulty in recognizing the picture. Only terror, 

 rage, or sharp pain could bring about precisely this condition. We. 

 have then in this property of reacting characteristically to condi- 

 tions involving strong emotions a feature of the thoracico-lumbar 

 system. 



This an Emergency Mechanism. At first thought there may 

 appear little utility in the characteristic reactions of excitement 



