538 PROFESSOR ALISON ON THE BELIEF 
Who hath given to our inward parts, or to our thoughts, the security of knowledge ? 
2. e., What security have we of the truth or reality of knowledge, which we can 
trace no farther than certain impressions made on, and changes excited in, our 
own minds? and the only answer which the context will admit is, that we have 
no security but the will of our Maker, whereby our minds are so constituted, that 
Belief is an essential component part of the acts which they uniformly perform, 
or the states which they uniformly assume, under certain circumstances ; which in 
this as in other departments of knowledge, we can go no farther than to specify 
and describe. 
I may just add, that there are two questions in Physiology, which have at- 
tracted much attention of late years, and of which I think a just view cannot be 
taken, without a previous accurate discrimination of those mental phenomena 
which Dr Rerp distinguished as Sensations, Perceptions, Recollections, and Volun- 
tary Efforts. The first regards the appropriation of the larger masses of the nervous 
system to their specific uses; and jirst, to those muscular movements which are 
generally now described as depending on the Refiex action of the Spinal Cord, e. ¢., 
those concerned in Respiration, Deglutition, and the various actions associated with 
those, and which have been ascertained, particularly by the experiments of 
FLourens, to have no dependence on the hemispheres of the Brain or Cerebellum ; 
and, accordingly go on, even for months together, in animals of which both the brain 
and cerebellum have been extirpated ; so that the term Reflex Spinal Action may be 
properly applied to them, instead of the older term Sympathetic Action, by which 
they were long previously distinguished. But it is equally certain, and was indeed 
established long ago, by Dr Wuyrr, that another principle is here concerned, 
which goes so far in explanation of the fact, not only that muscular contractions are 
excited by this reflex action in these circumstances, but that those muscles are se- 
lected for this purpose, which are capable of performing the motions, and successions 
of motion, requisite for the particular end to be attained in each case,—one set of 
motions, e.g., for breathing, another for coughing, another for deglutition, another 
for vomiting, &c. That principle is the existence and the peculiarity of the Sen- 
sation, preceding and attending the performance of each of these motions. The proof 
of this is, that in many of these cases, the same sensation may be excited by im- 
pressions made on the sensitive nerves of different parts, in each of which the 
same reflex or sympathetic movement follows; while in others, different sensa- 
tions result from varied impressions made on the sensitive nerves of the same 
parts, and in these different reflex actions are excited. It appears, therefore, that 
it is by the sensations preceding and attending them, that the nature and inten- 
sity of these reflex movements are determined, at least in the ordinary exercise of 
these functions ; and that those parts of the nervous system, and those only, which 
are found to be essential to those movements, must be those which are concerned 
