52 NERVOUS SYSTEM. 



A third class comprises those reflex actions whose centrip- 

 etal action is seated in the nerves of the sympathetic (ob- 

 tuse sensibility, called organic in the viscera), and whose 

 centrifugal course is that of the cerebro-spinal motor nerves 

 (vital relations) ; most of these phenomena belong to pathol- 

 ogy ; of this class are convulsions, which may be caused by 

 visceral irritations produced by intestinal worms, reflex 

 eclampsia, hysteria, etc.; as a normal phenomenon of this 

 kind, the respiratory reflex action may be cited, for the im- 

 pression that the pulmonary surface sends to the bulb is 

 transmitted by the pneumo-gastric ; which, under favorable 

 circumstances, is brought into relation with the nerves of the 

 great sympathetic, or, at least, forms a physiological passage 

 between the branches of the great sympathetic and those of 

 the cerebro-spinal system. 



Finally, a fourth and last class can be formed of reflex 

 actions whose ways of centripetal as well as centrifugal con- 

 duction are found in the filaments of the great sympathetic ; 

 we shall have to examine at another time whether the central 

 action for this class is located in the masses of gray matter of 

 the cerebro-spinal system, or in those of the ganglions of the 

 sympathetic chain ; of this class are the obscure reflex actions 

 and those which preside over the secretions of the various 

 intestinal fluids that are still difficult of correct analysis ; also 

 those which can partially explain to us the sympathies that 

 unite the various phenomena of the genital functions, espe- 

 cially in the female ; also the dilatation of the pupils from the 

 presence of intestinal worms in the digestive tract; and nu- 

 merous reflex pathological actions analogous to those already 

 Bpoken of. 



Laws of Reflex Actions. When a sensory impression 

 causes a reflex phenomenon, the production of this latter is 

 subjected in its intensity and anatomical distribution to cer- 

 tain precise rules, that Ffliiger first established by experimen- 

 tation on frogs (laws of Pfluger), and that Chauveau has 

 confirmed by his experiments on the great mammalia. Thus 

 a 'feeble irritation produced on the skin of the hinder extrem- 

 ities (for example, on the right side) causes a reflex movement 

 in the muscles of the same extremity, that is to say, in the 

 muscles whose motor nerves start from the spinal cord of the 

 same side and at the same height as the sensory fibres which 

 have been excited (law of unilaterality) ; if the excitation 

 becomes more intense, the motory reaction is manifested on 

 the opposite side, in the corresponding extremity : that is to 



