42 PHYSIOLOGY. 



functions ; for, by withdrawing that, as happens in the deliquiuni 

 animi, the functions of the brain and sensations disappear, I 

 think it probable that a certain tension is given to the substance 

 of the brain by the blood determined in such quantity to its 

 arteries, so that the sensibility of the brain and whole nervous 

 system connected with it, is increased by the increased impetus 

 of blood in the brain; e.g. in phrenitis the sensibility is increased, 

 because most of the organs of sense share in the increase 

 of impetus which gives the phrenitis. This impetus may 

 operate by giving more sensibility to the sentient extremities 

 themselves, but also by increasing the general sensibility of the 

 brain ; for this occurs also when the increased impetus has not 

 been extended to affect the sentient extremities. Gaubius, 

 treating of this subject says, in his Institutions, ( 194.) 

 ' A mente corpus irritabilius reddi non magis probabile est, 

 quam illam ab hoc incitarV This is again the Stahlian sys- 

 tem produced. I am willing to admit the modification of 

 Gaubius, (XXXI.) that the mind is ever the beginning of 

 motion in the body ; but we must, in physic, entirely abstract 

 from this, for the supposition is admitted to no purpose ; and 

 if we ever lose sight of the body as the object of physic, and 

 suppose an action of the mind independent of it, an operation 

 of the cause of which we cannot judge, we are quite thrown 

 out of our system. Gaubius says that the affection of the 

 body by the mind is not more probable than that of the mind by 

 the body. I say it is much less probable. In a thousand in- 

 stances we see that the body moves the mind, but in no one case 

 do we clearly see that the mind moves the body." 8. The state 

 of attention (XLVI. and XLVII.) " Lastly, I have to add 

 another cause : the sensibility of the sentient extremities may be 

 varied by causes of excitement or collapse (see CXXX.) direct- 

 ly applied to them. Of the causes of collapse operating directly 

 upon the sentient fibre, we have proofs in the action of sedative 

 or narcotic substances applied to them. Thus opium acts 

 upon every portion of the nervous system to which it is applied. 

 I am uncertain whether any powers of excitement exist, as I 

 cannot observe their operation or effect ; and we are not sensi- 

 ble of any powers but those which depend upon tension acting 

 upon the sentient extremities, There are, indeed, substances 



