General Principles of Physiology. 27 1 



of the brain lias the same effect. It was found that the division 

 of one of the eighth pair of nerves deranges the function of both 

 the stomach and lungs, nearly in the same degree with the de- 

 struction of a certain portion of the spinal marrow*. The func- 

 tion of every part of the brain and spinal marrow therefore is ne- 

 cessary to the due performance of secretion. 



Here a question of great importance in the animal economy 

 arises. As it appears, from the experiments just referred to, that 

 the nervous power is equally essential with the circulation of the 

 blood, for maintaining the functions of secretion and assimila- 

 tion, what are the parts they severally perform in these functions? 

 It is evident, that the extreme parts of the sanguiferous and 

 nervous systems are connected in a way very different from that 

 in which these systems are connected in other parts. The heart 

 and vessels of circulation, we have seen, can perform their func- 

 tion after the influence of the nervous system is withdrawn. 

 The function of the secreting vessels immediately ceases on the 

 interruption of this influence. We must suppose, therefore, 

 either that the influence of the nervous system bestows on the 

 extreme vessels the power of separating and re-combining the 

 elementary parts of the blood, or that the vessels only convey 

 the fluids to be operated upon by this influence. 



Experiments, to which I have already referred, prove that the 

 most minute vessels which can be seen by a powerful micros- 

 cope in the web of a frog's foot, are independent of the nerv- 

 ous system. The motion of the blood is as rapid, and the cir- 

 culation in the foot presents precisely the same appearance after 

 as before the slow destruction of the brain and spinal marrow. If 

 the power of the vessels of secretion had been lost by the in- 

 terruption of the influence of the nervous system, would not 

 this have necessarily occasioned some change in the distribu- 

 tion and motion of the blood in the web? The conclusion 

 from these experiments is strengthened by others. In those in 

 which the secreting power was destroyed either by the division 

 of the eighth pair of nerves or the destruction of part of the 

 spinal marrow, there did not necessarily appear to be a de- 

 ♦ Inquiry, Chap. vii. Sect. 2. 

 U2 



