THE NERVOUS SYSTEM. 



great length 9 that the brain is the origin of sensation and motion, 

 refuting the opinions of earlier days, as that of Chrysippus, 10 who 

 placed the hegemonic, or master-principle of the soul, in the heart. 

 But though Galen thought that the rational soul resides in the brain, 

 he was disposed to agree with the poets and philosophers, according 

 to whom the heart is the seat of courage and anger, and the liver the 

 seat of love." The faculties of the soul were by succeeding physiolo- 

 gists confined to the brain ; but the disposition still showed itself, to 

 attribute to them distinct localities. Thus Willis 13 places the imagi- 

 nation in the corpus callosum, the memory in the folds of the hemi- 

 spheres, the perception in the corpus striatum. In more recent times, 

 a system founded upon a similar view has been further developed by 

 Gall and his followers. The germ of Gall's system may be considered 

 as contained in that of Willis ; for Gall represents the hemispheres as 

 the folds of a great membrane which is capable of being unwrapped 

 and spread out, and places the different faculties of man in the 

 different regions of this membrane. The chasm which intervenes 



O 



between matter and motion on the one side, and thought and feeling 

 on the other, is brought into view by all such systems ; but none of 

 the hypotheses which they involve can effectually bridge it over. 



The same observation may be made respecting the attempts to 

 explain the manner in which the nerves operate as the instruments of 

 sensation and volition. Perhaps a real step was made by Glisson," 

 professor of medicine in the University of Cambridge, who dis- 

 tinguished in the fibres of the muscles of motion a peculiar property, 

 different from any merely mechanical or physical action. His work 

 On the Nature of the Energetic Substance, or on the Life of Nature 

 and of its Three First Faculties, The Perceptive, Appetitive, and 

 Motive, which was published in 1672, is rather metaphysical than 

 physiological. But the principles which he establishes in this treatise 

 he applies more specially to physiology in a treatise On the Stomach 

 and Intestines (Amsterdam, 1677). In this he ascribes to the fibres 

 of the animal body a peculiar power which he calls Irritability. He 

 divides irritation into natural, vital, and animal ; and he points out, 

 though briefly, the gradual differences of irritability in different 

 organs. "It is hardly comprehensible," says Sprengel, 14 "how this 



9 Lib. vii. la Lib. iii. c. 1. 



11 Lib. vi. c. 8. K Cuv. Sc. Nat. p. 384 



13 Cuv Sc. Nat. p. 434. H Spr. iv. 47. 

 VOL. II. 30. 



