Integrative Systems 189 



It appears that either contraction of muscles (items 3, 6, 7, 8) or 

 relaxation of muscles (items 2 and 5) may be associated with sympa- 

 thetic stimulation. Similarly, parasympathetic stimulation may be 

 followed by either contraction (items 2, 5, 7) or relaxation of muscles 

 (items 3 and 6). Sympathetic stimulation increases activity of sweat- 

 glands and decreases production of salivary and other digestive secre- 

 tions. On the whole, excitatory activity is more characteristic of the 

 sympathetic than of the parasympathetic, but there is no sharp dis- 

 tinction between them so far as the types of reaction are concerned. 



Double innervation — i.e., innervation from both divisions of the 

 autonomic system— occurs in most of the major viscera, but is much 

 more prevalent in coelomic than in somatic territory. While it is true 

 that nerves of either division may elicit a "plus" reaction in one organ 

 and a "minus" reaction in some other organ, there are two charac- 

 teristics in which the double innervation never departs from consist- 

 ency. First, in no case, so far as is known, do the nerves of the two 

 divisions elicit the same response from any one organ. Second, how- 

 ever inconsistent the two divisions may seem to be as to the nature of 

 their respective actions on the several organs, it is invariably true that 

 the resultant of their "antagonistic," but cooperative, actions on each 

 organ tends to enable that organ to perform the best possible service 

 for the animal under the circumstances which obtain at the moment. 

 And, further, the simultaneous autonomic controls of the several 

 organs are so correlated that the "grand total" result is such as to 

 enable the animal to do its most and best in times of stress and, with 

 the passing of the emergency, to return automatically to the physio- 

 logic economy of a period of peace. 



The distribution of sympathetic innervation is more extensive 

 than that of parasympathetic. The sympathetic penetrates into every 

 part of the body. Parasympathetic distribution is mainly coelomic, and 

 an organ so important as the uterus seems to be devoid of it. Con- 

 sistent with this difference in distribution, it is the sympathetic divi- 

 sion that plays the paramount role in periods of stress. It is, therefore, 

 given to large-scale operations, a wave of stimulation sweeping over 

 wide territories or the whole body. The parasympathetic is necessarily 

 more local in its action, and, within the territory of double innerva- 

 tion, it assists in restoring the routine working order after a period of 

 sympathetic excitation. 



To illustrate: when a cat is confronted by a menacing dog, rays of 

 light reflected from the dog stimulate the cat's retinal receptors. These 

 receptors initiate impulses which pass via the optic nerves to the optic 

 centers in the midbrain, whence they are relayed back through the 

 more posterior parts of the brain and then down the spinal cord to 



