THE AUTONOMIC NERVOUS SYSTEM 901 



These types of micturition must be set up by impulses which affect the 

 spinal centers in much the same way as impulses arising from the blad- 

 der itself. The bladder may consequently be emptied by three mecha- 

 nisms, (1) by its intrinsic activity as in Goltz and Ewald's dogs; (2) 

 by a purely spinal reflex through visceral afferent and efferent impulses, 

 and (3) through voluntary effort acting on the spinal centers and re- 

 inforced by the contraction of skeletal muscles. The former mechanism 

 is relatively inefficient, as is seen in the behavior of the bladder during 

 the failure of the reflex mechanisms which results from the shock of 

 a spinal cord injury. The urine is retained until the intravesicular pres- 

 sure becomes great enough to force the sphincter, and then it dribbles 

 out feebly. The bladder is not completely emptied and the residual 

 urine is apt to putrefy, giving rise to cystitis and other infections which 

 constitute the chief danger in such injuries. If the local condition of 

 the bladder remains good, the automatic emptying of the bladder may 

 become periodic and complete whenever about 225 c.c. of fluid accumu- 

 lates, even though the injury has completey destroyed the reflex con- 

 nection between badder and cord. If the injury to the cord does not 

 interfere with the reflex centers, recovery makes automatic reflex mic- 

 turition possible and the bladder is emptied completely at periodic in- 

 tervals as it becomes full, but is no longer under voluntary control 

 (Fearnside, 19 Head and Riddoch 20 ). 



The Function of the Thoracico-Lumbar Division. The thoracico-lum- 

 bar outflow, in contrast to the bulbo-sacral, inhibits the activity of the 

 digestive tract and brings about changes in the organs of circulation 

 which are appropriate to increased activity of the skeletal musculature 

 and of the nervous system which controls them. Whereas the different 

 parts of the cranial and sacral outflow are brought into activity sep- 

 arately, so that the digestive secretions may be stimulated without the 

 heart or iris being affected at the same time, and micturition may occur 

 independent of defecation, discharge over the thoracico-lumbar system 

 frequently has a diffuse nature, affecting all of the organs controlled 

 by it simultaneously. A definite syndrome consequently results which 

 is brought about under conditions of great emotion, as in fear, pain, 

 and rage. It consist of acceleration of the heart rate, constriction of 

 the arterioles in the skin and splanchnic viscera, inhibition of the mus- 

 cular activity of the gastrointestinal tract, inhibition of the salivary se- 

 cretion, erection of the hair and secretion of the sweat glands. These 

 changes occur under conditions when severe muscular effort is apt to 

 be exerted by the animal, and are appropriate because they tend to shift 

 the circulating blood to the muscles and nerves of the body at the ex- 

 pense of the viscera so that the maximum energy may be devoted to 



