HYDROPHOBIA; TETANUS; EPILEPSY; HYSTERIA. 503 



the severity of the convulsions. In tetanus there appears to be a simi- 

 larly excitable state of the Spinal Cord and Medulla Oblongata, not 

 involving the ganglia of special sense. This may be the result of 

 causes altogether internal, as in the idiopathic form of the disease ; in 

 which the condition exactly resembles that, which may be artificially 

 induced by the administration of Strychnine, or by its application to 

 the cord. Or it may be first occasioned by some local irritation, as 

 that of a lacerated wound ; the irritation of the injured nerve being 

 propagated to the nervous centres, and establishing the excitable state 

 in them. When the complaint has once established itself, the removal 

 of the original cause of irritation (as by the amputation of the injured 

 limb) is seldom of any avail ; since the slightest impressions upon al- , 

 most any part of the body, are sufficient to excite the tetanic spasm. 

 In like manner, Epilepsy, which consists in convulsive actions with 

 temporary suspension of the functions of the Encephalon, may result 

 from the irritation of local causes, like the convulsions of teething ; and 

 may, like them, cease when the sources of irritation are removed. But 

 when it becomes confirmed, it seems to involve a disorder of the nervous 

 centres, which no local treatment can influence. 



887. These and other forms of Convulsive disorder, when productive 

 of a fatal result, usually act by suspending the respiratory movements ; 

 the muscles which effect these being fixed by the spasms, so that the 

 air cannot pass either in or out, and suffocation takes place as completely 

 as if the entrance to the air-passages were closed. It is remarkable 

 that every one of them may be imitated by Hysteria ; a_ state of the 

 nervous system, in which there is a peculiar excitability, but in which 

 there is no such fixed tendency to irregular action, as would indicate 

 any positive disease, one form of convulsion often taking the place of 

 another, at short intervals, with the most wonderful variety. It will 

 often be found, that the convulsions may be immediately traced to 

 some local irritation ; thus they are particularly liable to occur at the 

 catamenial periods, especially if the menstrual flux be deficient ; but it 

 does not seem improbable, that here too the presence of morbid matters 

 in the blood has much to do with the development of that peculiar 

 excitability, which gives to slight local irritations such a powerful 

 agency. 



888. The statement that the Spinal Nerves arise by double roots, is 

 not without exception as regards some, which, arise from its cranial 

 prolongation, and which are distributed to the parts of the head and 

 neck. The first spinal nerve, or sub-occipital (the 10th pair of Willis) 

 not unfrequently arises by a single set of roots, from the anterior por- 

 tion of the cord ; and it is then purely motor, except in virtue of its 

 inosculation with other nerves. The Hypoglossal (9th pair of Willis) 

 appears to be also a purely motor nerve ; arising by one set of roots, 

 and being distributed entirely to the muscles of the tongue, which 

 organ derives its sensibility from other nerves. The Grlosso-Pharyn- 

 geal usually arises from a single set of roots, and these correspond 

 with the posterior roots of the spinal nerves ; in some animals, however, 

 and occasionally in man, there is a distinct anterior root, and the 

 nerve, acquires direct motor functions. It may in some respects be 



