THE SYMPATHETIC SYSTEM 189 



In the first, the lesion affects the spinal medulla, and the 

 sympathetic and the cerebro-spinal systems are involved 

 together. With regard to both systems, the amount of 

 paralysis depends on the nature and the level of the lesion. 

 The whole of the sympathetic system is paralysed in complete 

 lesions of the spinal medulla above the level of the first 

 thoracic segment, but the amount of paralysis is much less when 

 the injury occurs in the thoracic or lumbar regions (p. 190). 



In the second group, the sympathetic trunk is itself involved. 

 The lesion is usually due to the pressure of a tumour growth 

 and is consequently unilateral in most cases. 



(a) When the sympathetic trunk is involved between the 

 superior and the middle cervical ga?iglia, the sympathetic 

 supply to the head and neck is entirely cut off and the condi- 

 tion gives rise to certain well-marked and easily recognisable 

 symptoms, of which the most important are those in connec- 

 tion with the eye. (i) The dilatator pupillae muscle is paralysed 

 and the pupil on the affected side is therefore definitely con- 

 tracted. (2) In addition, owing to paralysis of the ciliary 

 bundle (p. 210), pseudo-ptosis develops together with 

 apparent narrowing of the palpebral fissure. (3) These 

 features are accompanied by a slight degree of enophthalmos, 

 for which no very satisfactory explanation has yet been brought 

 forward. (4) All the blood-vessels of the affected side of the 

 head and neck become dilated, and the resulting vascular 

 engorgement is seen best in the conjunctiva. (5) The salivary 

 and lacrimal secretions are usually increased in quantity in the 

 first instance, but they may -be deficient or even absent at a 

 later period. (6) The affected areas of skin become dry and 

 rough, owing to paralysis of the sweat-secreting glands. 



It should be remembered that tumour pressure at first pro- 

 duces an irritative lesion, causing stimulation rather than 

 paralysis of the sympathetic. In this event, the above- 

 described chain of symptoms is reversed. The pupil is widely 

 dilated, the skin areas sweat profusely, etc. 



(b) Lesions occurring at the middle cervical ganglion, or 



