INTRODUCTION XVil 
a local co-ordinating mechanism, but that this local mechanism was dominated 
by the central nervous system. 
In the course of these investigations Lister had under frequent observation 
the stellate pigment-cells of the frog’s skin, the concentration and diffusion 
of the chromatophorous particles within which produce the temporary varia- 
tions in colour of the animal. The diffusion of the particles throughout the 
stellate cells causes the tint to darken, whereas their concentration in the body 
of the cell produces the opposite effect. Lister noticed that when the animal 
struggled, the particles moved suddenly and energetically in the direction of 
the body of the cell, as if acted upon by some stimulus. Convinced that he 
was observing a vital phenomenon of great physiological importance, he deter- 
mined to investigate it. 
Von Wittich had found that the process was under the influence of the 
nervous system and that the sciatic nerve contained fibres which controlled 
the condition of the pigment-cells of the hind limbs. Lister confirmed these 
observations and further succeeded in demonstrating the mechanism of control, 
and showed that the adaptation of the colour of the frog to its surroundings 
was brought about reflexly by light entering the eye. 
Lister also made observations of the first importance upon the nervous 
mechanism of the musculature of the gut.2, These experiments were primarily 
undertaken to test Pfliiger’s conclusion that the splanchnic nerves contained 
special inhibitory fibres distributed to the muscular coats of the intestine. 
Lister verified Pfliiger’s results, but did not accept his interpretation. He 
came to the conclusion that both the observations of Pfluger and his own 
experimental results were not inconsistent with the view that the same fibres 
produce increased and diminished muscular activity, according to the strength ot 
the stimulus impressed upon them. Although later work has justified the inter- 
pretation of Pfliiger, the experiments devised by Lister to test this hypothesis led 
him to important conclusions regarding the mechanism of intestinal movements, 
namely, that there was an intrinsic nervous apparatus which co-ordinated the 
movements of successive muscular fibres in peristalsis, and that the latter could be 
stimulated or checked by impulses coming from other parts of the nervous system. 
Another department of physiology to which Lister made considerable con- 
tributions was the causation of the coagulation of blood.’ His attention seems 
to have been drawn to this subject by the coagulation of blood in an inflamed 
artery, and the question presented to him was, why does blood clot in contact 
with an inflamed vascular wall, whereas it remains fluid when surrounded by 
healthy endothelium ? 
TeVol. a: p- 48. * Vol. i, p. 87. * Vol. i, pp. 69, 105, 109, and 189. 
LISTER I b 
