SPECIAL PHYSIOLOGY. 51 



also of the phenomena which then took the name of reflex 

 (impressionum sensoriarum in motorias reflexio) (1784) ; 

 finally the histological study of the nerve globule, and its re- 

 lations with the elementary fibres, afforded an opportunity 

 of making a more exact account of the mode by which this 

 reflection is made, though in regard to this latter point most 

 of the facts are even yet quite hypothetical. Since that time 

 Marshall Hall, Mueller, Lallemand, Flourens, Longet, CL 

 Bernard, etc., have enriched science with facts numerous 

 enough to allow of the classification of the reflex actions, of 

 laying down the precise laws of their production, as well as 

 the influences that modify them (especially in regard to the 

 medullary reflex actions). 



Classification of Reflex Actions. These are divided 

 according to the direction followed by the centripetal and 

 centrifugal actions: these actions present two directions; 

 either the nerves of the cerebro-spinal system, which have occu- 

 pied our attention up to this point, or the branches of the 

 great sympathetic, which will terminate our study of the 

 nervous system. 



The most numerous of the reflex actions follow the centrip- 

 etal and centrifugal direction of the spinal nerve filaments ; 

 of this class, the larger portion we have already cited under 

 deglutition, sneezing, cough, walking, etc., and in pathology 

 a large number of morbid reflex actions, as vomiting, tetanus, 

 epilepsy, etc. 



A second class, almost as numerous, comprises those reflex 

 actions where the centripetal direction is in the course a sen- 

 sory nerve of the cerebro-spinal system, and the centrifugal 

 direction a motor-nerve of the great sympathetic, most often 

 a vaso-motor nerve ; of this class are the reflex actions which 

 give rise to most of the secretions (saliva, gastric juice, etc.), 

 to the phenomena of blushing, or pallor of the skin, to erec- 

 tion, to certain movements of the iris, to certain modifications 

 in the pulsations of the heart, and in pathology to a large 

 number of phenomena called metastatic, on account of the 



freat difficulty of accounting for the mechanism of their pro- 

 uction, as for instance a large number of ophthalmias, of or- 

 chitis, of coryza, which depend on a reflex hyperaemia ; and, 

 on the other hand, dependent on a reflex anaemia, as, for in- 

 stance, certain cases of amaurosis, paralyses, paraplegias, etc. 1 



1 Vide Ch. Rouget, Introduction to " Diagnostic et Traite- 

 ment des diverses especes de Paralysies des Membres Inferieurs." 

 By Brown- S6quard. Paris, 1864:. 



