68 THE PRINCIPLE OF THE DIRECT CHAP. Ill trembled to such a degree from delight, that he could not for some time reload his gun; and I have heard of an exactly similar case with an Australian savage, to whom a gun had been lent. Fine music, from the vague emotions thus excited, causes a shiver to run down the backs of some persons. There seems to be very little in common in the above several physical causes and emotions to account for trembling; and Sir J. Paget, to "whom I am indebted for several of the above statements, informs me that the subject is a very obscure one. As trembling is sometimes caused by rage, long before exhaustion can have set in, and as it sometimes accompanies great joy, it would appear that any strong excitement of the nervous system interrupts the steady flow of nerve-force to the muscles.2 The manner in which the secretions of the alimentary canal and of certain glands—as the liver, kidneys, or mammas—are affected by strong emotions, is another excellent instance of the direct action of the sensorium on these organs, independently of the will or of any serviceable associated habit. There is the greatest dif- ference in different persons in the parts which are thus affected, and in the degree of their affection. The heart, which goes on uninterruptedly beating night and day in so wonderful a manner, is extremely sensitive to external stimulants. The great physiologist, Claude Bernard,3 has shown how the least excitement of a sensitive nerve reacts on the heart; even when a nerve is touched so slightly that no pain can possibly fi" ' 2 Miiller remarks (£ Elements of Physiology,' Eng. translat. vol. ii. p. 934) that when the feelings are very intense, " all the spinal nerves become affected to the ex- tent of imperfect paralysis, or the excitement of trem- bling of the whole "body." * * Lemons sur les Prop, des Tissus Vivants,' 1866, pp. 457-466.