412 FUNCTIONS OF THE NERVES. [ch. iii. 



not appear to have the real stamp of truth, which I leave, 

 however, to be decided on by other perspicacious men, to 

 whose attention I would also commend this conjecture, namely, 

 whether when the vis nervosa is increased by a stimulus, it 

 does not render the force of attraction of the fluids circulating 

 through the vessels greater, so that by this means the fluids are 

 attracted from every side to the centre of stimulation, as occurs, 

 for example, when sealing-wax is gently rubbed on a piece of 

 cloth, and made electrical, and attracts sand and particles of 

 various kinds? Speculations of this kind are not vain and 

 useless, because if the true reason be known why the nerves 

 when stimulated cause accumulation of the fluids in the tissues 

 to which they are distributed, much light will be thrown on 

 the nature of the vis nervosa itself, for one truth leads to another. 



living or dead, and is so great that it appears to be a power quite sufficient to restore 

 the artery to its former condition after being dilated by the blood sent into it from 

 the heart, and to pass that blood onwards to the veins : it is by this elasticity only, 

 that the systole of the arteries so immediately and quickly follows the systole of the 

 heart, as happens in the regular and natural pulse ; while, on the contrary, the irri- 

 tability of arteries is small, requiring the strongest stimulus, and not always respond- 

 ing to this, so that it obviously appears inadequate to the repeated natural systole 

 of the arteries. According to the experiments of Haller (De Part. Corp. Hum. Fabr. 

 et Funct., tom. iv, pp. 93, 289), it is only the elasticity of the arteries, which, after 

 the death of an animal, impels the blood from every point through a wound, since 

 all irritability had disappeared. As the irritability of arteries, according to the ex- 

 periments of Verschuir, is hardly excited even by very acrid stimuli, it will scarcely 

 be developed by the unstimulating blood sent from the heart into the artery ; but it 

 seems to presuppose great disturbance of the nervous system, by which it is excited. 

 This takes place differently in different parts, and to it, perhaps, ought to be ascribed 

 those abnormal pulsations, diflferent in different parts, and even complete pulse- 

 lessness ; examples of which, given by authors worthy of credit, are cited by Verschuir 

 in the Dissertation just noticed, and by Gruber in his Dissertation * De Excessu Vis 

 Vitalis,' published in Klinkosh's collection of disputations at the University of 

 Prague. Consequently, it appears to me, that the natural systole of the arteries 

 ought to be attributed to their elasticity only ; but as to the cause of the different 

 pulses in different parts, observed in the same individual at the same time, and also 

 as to the want of pulsation in pulselessness, it is clearly demonstrated by the experi- 

 ments of Verschuir to be the irritability of the arteries. Whence it therefore follows, 

 that arteries in their natural condition react solely by their elasticity, and are not 

 irritable ; but that they become irritable and contract, in a preternatural condition, 

 when the vis nervosa of the nerves distributed to the arteries is preternaturally in- 

 creased ; or when a very powerful stimulus, as in the experiments of Verschuir, is 

 applied to them ; and we have additional confirmation of this, when we remember 

 that some parts of our bodies, which are without sensation in the natural state, be- 

 come extremely sensitive in disease. 



