898 CENTRAL NERVOUS SYSTEM 



gastrointestinal tract carries out its rhythmic movements and maintains 

 polarity in its action after it is separated from its extrinsic nerve supply. 

 Even the mechanism for operating the pyloric sphincter does not de- 

 pend on nervous connections extending beyond the gut wall. The secre- 

 tion of the gastric, pancreatic and intestinal juices is also brought about 

 by hormones of the secretin type so that nerves are unnecessary for this 

 activity. 



Goltz and Ewald have succeeded in keeping dogs alive and in good 

 condition for long periods after removal of the spinal cord below the 

 cervical region. After such animals have recovered from the immediate 

 effects of the operation, the skeletal musculature of the posterior part 

 of the body is paralyzed and soon atrophies. The organs under auto- 

 nomic control recover their normal function to a surprising extent. The 

 tone of the blood vessels recovers, and they react to temperature changes 

 much as a normal vessel would. The digestion becomes normal, defeca- 

 tion takes place regularly, and the bladder is emptied periodically and 

 spontaneously. A pregnant bitch gave birth to puppies a few hours 

 after 9.4 cm. of cord had been removed, and suckled one of them suc- 

 cessfully. In these animals it appeared that the organs innervated by 

 the autonomic nervous system could function successfully after the cord, 

 and with it the connector neurons, had been destroyed. The experiments 

 suggest that the autonomic system may contain reflex arcs within itself, 

 which do not pass into the central nervous system. A difficulty arises 

 here because it has not been possible to demonstrate any connection in 

 the outlying* ganglia between the afferent fibers passing through the 

 autonomic nervous system and the effector neurons. 



A type of reflex which may operate here is that known as the axon 

 reflex. The only axon reflex which is known to function, except under 

 laboratory conditions of stimulation, affects the cutaneous blood vessels, 

 and causes a local inflammation to be set up in the skin when mustard is 

 applied to it. This reaction was shown by Bruce to persist after cutting 

 the dorsal roots of the spinal nerves and consequently could not be attributed 

 to a spinal reflex. After the sensory fibers had degenerated, however, 

 the effect could no longer be elicited. It appears from this that the 

 mechanism depends on the integrity of the peripheral end of the sensory 

 fibers. It is believed that these send off collaterals which connect with 

 the cutaneous blood vessels. Impulses set up by the mustard in the 

 sensory termination pass up the fiber to these collaterals and down them 

 to the blood vessels where dilation is produced. This mechanism also 

 explains the observation of Bayliss that stimulation of the peripheral 

 stump of the dorsal root of a spinal nerve causes a local vasodilatation 

 in the skin. A similar axon reflex has been found to occur in certain 

 connector fibers of the thoracico-lumbar outflow which supply the smooth 



