Diseases of tke Internal Senses. 743 



lead in the system lead poisoning. In these cases, and in most cases 

 of epilepsy and hysteria, the sensory ganglia are thought to be chiefly, 

 if not exclusively, involved, because there is not such confusion of 

 ideas as should be expected from a disturbance of the cerebral tissues. 

 Epilepsy, according to Dr. Todd, arises from defective nutrition of cer- 

 tain parts of the brain centers, which causes a gradual disturbance of 

 their polar state. This produces a tension of nervous energy, which 

 periodically becomes too strong for restraint, and discharges itself in 

 the epileptic paroxysm. 



Chorea, or St. Vitus dance, is a disease in which the cerebral influ- 

 ence over the movements of certain parts, is much diminished, while 

 the parts are still left subject to the stimulation of the sensory (basal) 

 ganglia. The result is an irregular and ungoverned movement of the 

 muscles of the limbs, trunk or face. These movements do not continue 

 during sleep, and they are apt to be exaggerated by emotions. The 

 disease is usually preceded and accompanied by imperfect nutrition, a 

 depraved state of the blood, and torpor of the s}'stem. 



Coma is a state in which the sensory ganglia are chiefly, if not ex- 

 clusively, involved. Their functions are more completely suspended 

 than in sleep, and no impressions are conveyed to them from the out- 

 side. The cerebrum does not appear to be involved generally, because 

 there is no confusion of ideas following the comatose state. In hyster- 

 ical patients sometimes the state of insensibility comes on suddenly, 

 even in the midst of a sentence, which is being uttered. On the return 

 of consciousness the person will go on and finish the sentence as if no 

 interruption had taken place, and in fact he is not conscious that there 

 had been an interruption. Coma is induced by narcotic poisons, the 

 same which in smaller and less intense measure would produce delirium; 

 also by exhaustion and a deficient supply of blood, and by concussion 

 of the brain. In all cases, the cause seems to be due to deficient blood 

 supply. Coma acts like sleep in affording an opportunity for the re- 

 pair of the brain tissues worn out by excessive mental action, or other 

 injury. There are many cases on record, of protracted sleep lasting 

 for many days and even weeks. Such cases seem to be allied to hysteric 

 coma, rather than to natural sleep. An unusual tendency to ordinary 

 sleep indicates a congested state of the brain, a deficiency of blood, 

 which tends to apoplexy ; and it is said that apoplexy has been actually 

 induced by the experimental attempt to protract sleep as long as possi- 

 ble. ( Carpenter. ) 



The total disuse of an organ causes the atrophy of the nerve and 

 brain cells exclusively belonging to it. In fig. 377 is shown a wasted 

 optic nerve consequent upon permanent blindness in the left eye, while 

 the left nerve is nearly normal. In this case the wasting is traceable 



