SECT. 11.] ACTION OF THE NERVES ON THE VESSELS. 411 



that distinguished man propounds a peculiar and singular con- 

 jecture, which appears to me, however, unfounded, to the effect 

 that since a stimulus has quite a different result on the mus- 

 cular arteries, than on the heart and other muscles — inasmuch 

 as the arteries appear to be dilated by a stimulus, whereas we 

 see that the heart and other muscles to be contracted — he 

 thinks that the blood is attracted, and flows from all sides into 

 the arteries dilated by a stimulus. An opinion of other eminent 

 men, as to the cause of the derivation of the fluids to a stimu- 

 lated part is, that the stimulus renders the arterial action 

 more frequent and powerful, consequently that the arteries carry 

 a greater quantity of the fluids onwards than the veins can return, 

 and thus they explain why the fluids should accumulate more 

 copiously in a stimulated part.^ But even this doctrine does 



* I may be permitted to make some observations here on the irritability and mus- 

 cular contraction of arteries. The experiments of Haller appeared to render the irri- 

 tability of arteries doubtful, as he never found them irritable ; and to show that the 

 systole of the pulsating arteries in the natural state arises solely from their elasticity, 

 by which they are restored to their former condition after being distended by the 

 blood projected from the heart, and enabled to transmit the blood thus received 

 inwards into the veins, so that along with the eminent men who have repeated the 

 experiments, I expressed my assent to their validity in * Controversis Quaestionibus 

 Physiologicis,' p. 30. The experiments of Verschuir on the irritability of arteries, 

 were not then known to me ; they are contained in his Dissertation ' De Arteriarum 

 et Venarum vi irritabili ejusque in vasis excessu ; et inde oriunda Sanguinis direc- 

 tione abnormi,' printed at Grbningen in 1766, and fully demonstrate that some- 

 times arteries and veins manifestly contract on the application of a powerful 

 stimulus, as scraping with a scalpel, oil of vitriol, spirit of sal ammoniac, &c. ; but 

 generally the contractions were very indistinct, and not unfrequently neither re- 

 sponded to these acrid stimulants, nor, as in the experiments of Haller, could 

 irritability be detected. It is also shown from all these experiments of Verschuir, 

 when properly collated, that although arteries were found to respond to these 

 acrid stimulants in one or more places, in another part of the same animal it 

 was the least possible. Further, it is to be observed, that those contractions which 

 were excited continued for some time before they ceased, and the artery was re- 

 stored to its former condition ; consequently the contraction and relaxation of the 

 artery did not follow each other so quickly as the systole and diastole of the artery 

 in its natural condition, nor as quickly as the heart, when irritated, contracts and 

 then immediately relaxes. Lastly, it also appears from the experiments of this dis- 

 tinguished physiologist, that a portion of an artery, which an acrid poison had 

 caused to contract, was hard and rigid, and no longer pulsated ; while, at the same 

 time, other portions of the same artery, untouched by the acrid stimulus, continued 

 to repeat their pulsations. But are the results of these experiments opposed to the 

 doctrine, that the elasticity of the arteries is the cause of their systole ? By no 

 means ; for the elasticity of the arteries is ever demonstrable in any animal, whether 



