53 



continued to apply himself assiduously to original scientific research, 

 and physiology, especially in its relations to medicine, was his favourite 

 pursuit. In 1831 he published his " Essay on the Circulation of the 

 Blood," which contains observations on the flow of blood in the 

 capillary vessels of Batrachia and Fishes, and on the characters by 

 which these vessels are distinguished from arteries and veins. On 

 this occasion he made known his discovery of a remarkable pulsa- 

 ting sac or "caudal heart " connected with the vessels in the tail of 

 the eel. The results of further physiological inquiries were published 

 in the Philosophical Transactions for 1832, in two papers, one "On 

 the Inverse Ratio which subsists between the Respiration and Irrita- 

 bility in the Animal Kingdom," the other "On Hybernation ; " and 

 a few years later he contributed the articles "Hybernation" and 

 "Irritability" to Dr. Todd's Cyclopeedia of Anatomy and Physiology. 



But his name will hereafter be best known in connexion with the 

 doctrine of the Reflex Function of the Nervous System, which was 

 his most engrossing subject of pursuit for the last twenty-five years 

 of his life. In the Philosophical Transactions for 1833 appeared his 

 " Memoir on the Reflex Function of the Medulla oblongata and Me- 

 dulla spinalis," the object of which is to show that certain involun- 

 tary acts previously designated as " sympathetic motions " are excited 

 by impressions made on the extremities of certain nerves, arid con- 

 ducted by them to the spinal marrow and medulla oblongata, whence 

 as from a centre they are reflected on the motor nerves of the parts 

 moved ; that these motions are concerned especially in various func- 

 tions which are necessary for the preservation of the individual or of 

 the species, and that they are independent alike of sensation and 

 volition ; moreover, that the " tone " of the muscular system belongs 

 to the same order of phenomena and depends on the spinal marrow ; 

 lastly, that the reflex function may be exalted or depressed by medi- 

 cinal agents, and in its abnormal or morbid conditions give rise to 

 various well-known spasmodic, convulsive, and other nervous diseases. 



Dr. Hall admitted that the phenomena of which he treated had 

 long been known to physiologists, but he believed himself to have 

 been the first to show their independence of sensation, to bring them 

 together under one generalization, to establish with precision the laws 

 of their production, to assign them their just rank in physiology, and 

 to apply the doctrine to the elucidation of disease. But while we do 



