CH. II.] EXTERNAL DIRECT NERVE-ACTIONS. 245 



the alteration of the pulse, when the blood is at a higher tem- 

 perature, or has undergone a morbid change, is connected 

 therewith, the nerves and muscular fibres being irritated by the 

 morbid blood, so that the arteries contract more forcibly and 

 quickly; which action must be a direct nerve-action, excited by 

 an external impression of an unnatural kind. The reader is 

 recommended to take into consideration the proofs of the irri- 

 tability of arteries, adduced, from his own researches, by 

 Verschuir, in his excellent dissertation, " De Arteriarum et 

 Venarum vi irritabili/^ &c. — Groningen, 1766. However, 

 whether the natural movement of the arteries be simply me- 

 chanical, or whether it be a direct nerve-action of external 

 impressions received from the in-streaming blood, in either 

 case it is independent of the brain or the mind. Lastly, since 

 every assistance which is given to the circulation in the blood- 

 vessels of the muscles by muscular action (169), maybe as often 

 the result of a direct nerve-action of an external impression on 

 the muscles as of a sentient action; it may be asserted, that 

 the entire circulation of the blood, and the functions, and 

 changes in organs mechanically connected therewith, may be 

 carried on without the co-operation of either the brain or the 

 mind, and, in fact, are so carried on, even in animals endowed 

 with consciousness. 



461. This is proved by experiment. In animals which do 

 not bleed to death immediately after decapitation, the beat of 

 the heart and the pulse, and the entire circulation (so far as 

 the great disturbance of the organism admits of) goes on un- 

 interruptedly for a considerable period (Haller ^ Opera Minora,^ 

 torn, i, p. 425), and are altered by external stimuli, especially 

 by the various qualities of the blood. The arterial pulse, in 

 cases of suffocation, when life is restored by artificial means, 

 returns only after the hearths action is established, and is first 

 felt in the vessels nearest to the heart. In the dying and in 

 syncope, the pulse continues in the latter vessels, when it can 

 be no longer perceived in the more distant. 



462. The arterial capillaries, as has been already shown 

 (207), are capable of special movements, which although some- 

 times sentient, belong properly to the class of direct nerve- 

 actions, excited by external impressions on the nerves which 

 surround these vessels. They consist in this, that an external 



