REFLEX ACTION AND DISEASE. 639 



omitted here on account of the detailed description that would be re- 

 quired to make them intelligible. 



Naturalists should not be slow to appreciate the conscientious labor 

 which alone has led Mr. Hyatt to these results, or to follow up the line 

 of investigation which he has opened. 



♦«» 



KEFLEX ACTION AND DISEASE. 



By T. LAUDER BRUNTON, F. R. S. 



AS a preliminary to the paper of this evening upon reflex action as a 

 cause of disease and a method of cure, I must say a word about 

 reflex action itself, and also about another subject with which it is very 

 closely connected, viz., the transference of impressions. 



Reflex action is the eS"ect produced by an impression made upon a 

 sensory nerve, transmitted by that nerve to a nerve-center, and reflected 

 or thrown back along a motor nerve in much the same way as we may 

 imagine the force to be which is applied to one end of a string running 

 over a pulley and transmitted in a different direction by the other end 

 to produce a certain effect. If we fancy the farther end of the string 

 to be divided into several strands, each of which js attached to a differ- 

 ent object, and which may be, separately or together, afi'ected by a pull 

 on the nearer end of the string, we shall form a still more definite notion 

 of reflex action, for an impression made upon the same sensory nerve may 

 produce various results, according to the strength of the impression and 

 the efi'erent nerve-channel along which it is thrown back by the nerve- 

 center. An impression made upon a sensory nerve, for example, may 

 produce motion of either a voluntary or involuntary muscle, or may 

 afiect the nutrition of a tissue. Under the head of involuntary muscles 

 we must class the muscular fibers of the vessels, and those vascular 

 changes which in themselves play a great part in nutrition and secre- 

 tion may be very greatly influenced by impressions made upon sensory 

 nerves. The way in which we know that the nutrition of a tissue may 

 be influenced reflexly apart from the changes in the vessels is, that ob- 

 servations on the submaxillary gland have demonstrated that we may^ 

 under certain conditions, obtain vascular changes without the secretion 

 which usually accompanies them, and that, vice versa, we may obtain 

 secretion without the vascular changes which ordinarily accompany it. 

 Thus, on stimulating the nerves of the tongue, the impression which we 

 make is usually transmitted by the fifth nerve to the brain, and is thence 

 reflected down the chorda tympani to the submaxillary gland. There 

 it induces dilatation of the vessels, and free secretion of saliva from the 

 gland. But if we administer atropia we do away with one of these 

 1 Read before the Abernethian Society, St. Bartholomew's Hospital. 



