NERVOUS INTEGRATIONS IN MAN 255 



of the hind foot, and this occurs after severance of the 

 spinal cord. The shoulder-skin irritated by parasites then 

 evokes still the same scratching movement of the hind 

 Hmb, although both the skin and the muscles are beyond 

 means of appeal to any portion of the brain. The scratching 

 thus performed as a pure spinal reflex does however often 

 lack the precision of direction which higher and cerebral 

 control can give it. Instances in normal man of simple 

 protective reflexes are, besides the closure of the eyelids 

 against a blow, the expiratory movements, cough and 

 sneeze, which remove irritants from the respiratory passage; 

 also the involuntary holding of the breath against an irritant 

 vapor. The purposive character of reflexes is evident. 



In man severance of the spinal cord is followed imme- 

 diately by a period of depression of function in that part of 

 the cord cut off" from connection with the brain. This period 

 of shock lasts for weeks or months. It is as though in man the 

 higher nervous centers so greatly contribute to the driving 

 of the spinal (lower) mechanisms that the removal of that 

 drive upsets the spinal mechanisms for a long time. In 

 most animals this is far less so, e.g. dog; but the monkey 

 in this respect resembles man. In man the spinal reflexes 

 released from higher control tend to be mainly flexor in 

 type. There is a spread from one spinal center to another, 

 so that contraction of the bladder, and profuse sweating 

 may accompany flexion of both legs; this generalized spinal 

 reflex response is termed the "mass reflex." 



The Decerebrate Animal. We may now pass from the 

 spinal condition in man to a more highly integrated state, 

 usually referred to as the decerebrate condition. The 

 condition, which is brought on by removal of the nervous 

 organ anterior mid-brain is well recognized in animals 

 and has been thoroughly investigated. (See Chapter iv.) 

 A decerebrate animal is capable of standing albeit the 

 posture is an exaggerated caricature. Movements are well 

 coordinated and graded so long as the cerebellum remains 

 intact. The decerebrate condition is also characterized 

 by a series of striking reactions known as the neck and 

 labyrinthine reflexes. Rotation of the head to the left, 

 for example, causes increase in tonus of the extensor muscles 



