278 ANIMAL PHYSIOLOGY. 
It is stated that in course of time the vessels of the rabbit’s 
ear regain their tone, notwithstanding that the influence of the 
Vaso-motor Center in 
Medulla. 
Spinal Cord 
Efferent Vaso-rmotor 
Nerve. 
Outlying Vascular 
Area. 
Afferent Nerve from 
Periphery. 
Fig. 243.—Diagram of nervous vaso-motor mechanism. I. Course of afferent impulses from 
the heart itself along the a kee nerve. II. Course from some other part of the brain. 
Ill. Course from some peripheral region along a nerve joining the spinal cord. The effer- 
ent impulses are represented as passing to a vascular area, reduced for the sake of sim- 
plicity to a single arteriole. 
central nervous system has been cut off by section of the vaso- 
motor nerves. 
To explain this result, a local nervous mechanism has been 
assumed to exist, though not demonstrated either anatomically 
or physiologically. Interesting experiments have lately shown 
that both in mammals and cold-blooded animals the effect on 
the blood-vessels varies with the intensity and character of the 
stimulus, and not only with the group of animals tested, but 
even with the same individuals at different periods during the 
experiment ; and we take the opportunity to renew our expres- 
sion of opinion with this fresh evidence that the laws of physi- 
ology can not be laid down in the rigid way that has prevailed 
