Cuss III. 2. 1. 10. OF VOLITION. 337 



for many minutes without attempting to drink, or withdrawing 

 his hand. He never spoke, and it was at first necessary to 

 compel him to drink broth; he recovered in a few weeks with- 

 out relapse. 



10. Hemiplegia. Palsy of one side consists in the total dis- 

 obedience of the affected muscles to the power of volition. As 

 the voluntary motions are not perpetually exerted, there is little 

 sensorial power accumulated during their quiescence, whence 

 they are less liable to recover from torpor, and are thus more 

 frequently left paralytic, or disobedient to the power of volition, 

 though they are sometimes still alive to painful sensation, as to 

 the prick of a pin, and to heat; also to irritation, as in stretch- 

 ing and yawning; or to electric shocks. Where the paralysis 

 is complete, the patient seems gradually to learn to use his limbs 

 over again by repeated efforts, as in infancy; and, as time is re- 

 quired for this purpose, it becomes difficult to know, whether 

 the cure is owing to the effect of medicines, or to the repeated 

 efforts of the voluntary power. 



The dispute, whether the nerves decussate or cross each other 

 before they leave the cavities of the skull or spine, seems to be 

 decided in the affirmative by comparative anatomy; as the op- 

 tic nerves of some fish have been shewn evidently to cross each 

 other; as seen by Haller, Elm. Physiol. t. v. p. 349. Hence 

 the application of blisters or of ether, or of warm fomentations, 

 should be on the side of the head opposite to that of the affected 

 muscles. This subject should nevertheless be nicely determin- 

 ed, before any one should trepan for the hydrocephalus inter- 

 nus, when the disease is shewn to exist only en one side of the 

 brain, by a squinting affecting but one eye; as proposed in 

 Class I. 2. 5. 4. Dr. Sommering has shewn, that a true decus- 

 sation of the optic nerves in the human subject actually exists, 

 Elem. of Physiology by Blumenbach, translated by C. Caldwell, 

 Philadelphia. This further appears probable from the oblique 

 direction and insertion of each optic nerve, into the side of the 

 eye next to the nose, in a direct line from the opposite side of 

 the brain. 



The vomiting, which generally attends the attack of hemiple- 

 gia, is mentioned in Sect. XX. 8. and is similar to that attend- 

 ing vertigo in sea-sickness, and at the commencement of some 

 fevers. Black stools sometimes attend the commencement of 

 hemiplegia, which is probably an effusion of blood from the 

 biliary duct, where the liver is previously affected; or some blood 

 may be derived to the intestines by its escaping from the vena 

 cava into the receptacle of chyle during the distress of the para- 

 lytic attack; and may be conveyed from thence into the intes- 



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