574 
obliged to interpose an active cause between the impression on the 
afferent nerve and the motor influence in the efferent nerve, inas- 
much as no consistent attempt had then been made to assign separate 
offices to particular parts of the nervous centre ; and the idea that 
a part of the tissue of the nerves and brain (such as the white fibres 
in both), might be merely conducting cords, while another part, such 
as the grey substance, might be the exclusive origin of force, had 
not then arisen, whence, as he himself states, that his view was un- 
satisfactory to explain why an afferent nerve bringing an impres- 
sion from an external part to one point of the nervous centre, should 
have its effect reflected into an efferent nerve arising at a distant 
point of the same centre, unless some influence pervading the whole 
nervous centre, and therefore the space between the two nerves, were 
the exciting force, such as his sentient principle. 
The Memoir further shows, that though Whytt did not attempt 
to assign separate offices to separate parts of the nervous centre, 
understood as including the encephalon and spinal marrow, yet, 
when explaining the movements in decapitated animals, he suggests 
the idea that the spinal cord may be capable of independent action, 
as in tortoises, which live months after being deprived of the brain ; 
while it also affords proof that though Whytt made no pretensions 
to improve the anatomy of his age as respects the nervous system, 
he was the authority referred to for seventy years for the hypothesis 
now recognised as an important fact, — namely, that the ultimate 
fibrils of the nerves, amidst all their combinations into cords, plex- 
uses, and the like, pass unbranched and isolated from their origin 
to their termination. Again, it is maintained that this hypothesis 
could not fail by a single step to suggest the division of the nervous 
system into conducting cords and centres of force, and therefore to 
lead to the perception of the probable analogy between the gan- 
glionic system in the in vertebral animals and the nervous centre in 
the vertebrata. 
The sum of Whytt’s view is next exhibited in the Memoir in 
contrast with the matured state of the same doctrine in the present 
day, in as far as regards the non-vital involuntary movements,-— viz., 
the closing of the pupil under a strong light ; the shutting of the 
eyelid when the eye is threatened ; the adjustment of the mem- 
branes of the internal ear by the muscles of the tympanum to the 
variations of sound ; the act of respiration, and its modifications, 
