SUMMARY, MAMMALIAN NERVOUS SYSTEM; SPINAL SHOCK 965 



tivities are no longer correlated to the activities of the body as a whole. 

 The extent to which the spinal cord is capable of carrying out co- 

 ordinated neuromuscular activity, when isolated from the higher centers 

 of the brain is a matter of great interest. We have seen in considering 

 the mechanisms by which reflex action is governed that the spinal cord 

 contains arrangements capable of producing highly integrated responses. 

 We will consequently examine the activities of the isolated spinal cord 

 in laboratory animals, and compare them with similar conditions which 

 are observed in man, in order to obtain an idea of the relative importance 

 of the spinal cord and brain which show some diversity in their devel- 

 opment. 



Spinal Shock and the Recovery of Reflexes in Animals 



In animals the spinal cord may be separated from the brain by an 

 incision made in the cervical region. Immediately after the operation 

 a profound condition of depression sets in, involving all the reflex arcs 

 in the separated portion of the cord. This condition is known as spinal 

 shock. It supervenes in all classes of animals having a spinal cord, but is 

 much more profound in the higher than in the lower animals. As a result 

 of this depression, the part of the body below the section exists in a limp 

 and flaccid condition, and the application of even very strong stimuli to 

 the skin will evoke no form of reflex movement. In the case of the lower 

 vertebrates, such as the frog, the condition begins to pass off in from twenty 

 minutes to half an hour, after which a stimulus applied to the skin of the 

 foot is followed by a typical flexion movement at knee and hip, the so- 

 called flexion reflex. In the rabbit very little reflex response is elicitable 

 for several hours after the operation, but in a few days the reflexes return 

 completely below the level of the section. In the dog, on which a great 

 deal of work has been done, the involved regions of the body are pro- 

 foundly paralyzed. The skin is in a more or less unhealthy, unnatural 

 condition, the surface cold, the hairs ruffled; and if care is not taken, the 

 slightest abrasion of the surface may result in a nasty ulceration. On 

 account of the paralysis of the centers of micturition and defecation, 

 there is also incontinence of urine and of feces. 



With reasonable attention, however, the dog makes a wonderful re- 

 covery. After an interval of two weeks the hind limbs, although com- 

 pletely paralyzed so far as voluntary movement is concerned, begin to 

 show considerable signs of improvement. The first reflexes to return 

 are those concerned with the deeper structures, such as the vascular 

 reflexes, thus bringing the skin back to its normal temperature and 

 condition. The reflexes of micturition and defecation also soon return, 

 so that the animal no longer suffers from the continuous discharge of 



