130 The Unity of the Organism 



autonomic, because it is largely made up of fibers from the 

 vagus, or tenth pair of cranial nerv^es. Another is the sym- 

 pathetic, or better, the thoracico-lumbar autonomic, be- 

 cause its fibers originate from the great visceral sympathetic 

 ganglia. This is by far the most extensive of the three sub- 

 divisions, and is the only one that is distributed to all parts 

 of the body. The third is the sacral autonomic. As its name 

 implies, it is quite restricted in extent, its fibers being dis- 

 tributed to the extreme distal end of the intestine, the urin- 

 ary bladder, and some of the external genital organs. But 

 the differences between the three which are most important 

 for us are physiological, a particularly important difference 

 being that the thoracico-lumbar di\'ision acts antagonistic- 

 ally to both the end divisions. Stimulation of the fibers of 

 the sympathetic has just the opposite effect to the same 

 stimulus applied to the fibers of the others. "The sympa- 

 thetic fibers check, the vagal autonomic fibers excite, the 

 movements of the intestines ; the sympathetic dilates, the 

 vagal autonomic contracts, the pupil ; the sympathetic 

 hastens, the vagal autonomic slows, the heart." ^^ The 

 sacral contracts the lower part of the large intestine and re- 

 laxes the outlet of the bladder, while the sympathetic relaxes 

 the same part of the intestine and contracts the same part 

 of the bladder. Cannon states the general principle thus : 

 ''When the mid-part meets either end part in any viscus 

 their effects are antagonistic.'* ^^ 



While the incompleteness of knowledge in this field needs 

 emphasizing, yet that knowledge is sufficient to put some of 

 the main features beyond question, and to make clear the 

 great importance of the subject and of fuller knowledge on 

 it. Touching these general aspects Professor L. F. Barker 

 writes : "While we do not yet understand the exact mechan- 

 isms of association among the activities of the cerebrum, 

 the endocrine glands, and the reciprocally antagonistic au- 

 tonomic domains and their end-organs, we can begin to see 



