INFANTILE PAEALYSIS. 217 



in these muscles is a simpler matter. Cervical myelitis in the 

 region of the fourth segment causes paralysis of the diaphragm, 

 and since the impulses to the intercostal muscles are also blocked 

 by the same lesion, death results from respiratory failure. A 

 cervical myelitis is also liable to spread to the adjacent medulla 

 involving the vital centres in this region. 



A myelitis so situated as to involve the region of the cervical 

 cord which supplies the arm may give rise to alterations in the 

 size of the pupil, as will be explained in the section on 

 compression of the cord. 



It is not easy to give a simple description of the way in which 

 cord inflammations affect the mechanism of the urinary bladder. 

 If that part of the cord corresponding to the origin of the third 

 and fourth sacral nerves be involved there is no power to retain 

 the urine, which dribbles away almost as soon as it enters the 

 bladder, because the sphincter is paralysed. When the lesion is 

 at the junction of the dorsal and lumbar regions there is reten- 

 tion with overflow. When the lesion is above the ninth dorsal 

 segment the act of micturition may occur automatically as soon 

 as a fair quantity of urine has accumulated in the bladder, the 

 patient being quite unconscious of the act. In this case all the 

 local bladder centres are intact, but their higher connections are 

 severed. 



ACUTE ANTERIOR POLIOMYELITIS. 



This disease, commonly known as infantile paralysis, is due 

 to an acute lesion of the motor cell groups of the anterior 

 cornua of the spinal cord. The grey matter of the anterior 

 cornua, and also that forming the base of the posterior cornu, is 

 supplied with blood by branches derived from the anterior 

 spinal artery, so the lesion occurs in the territory supplied by 

 that vessel. (Fig. 19, p. 222.) The febrile onset of the disease 

 suggests an infective inflammation, but in a few of the cases 

 there is no fever, and this has led to a suggestion that these may 

 be of thrombotic origin. 



The motor cells of the anterior cornua are arranged in definite 



