SECT. II. PHYSIOLOGY. 15 
In paralytic extremities it would, however, appear, 
that the nerves require a stronger excitement 
than that of the blood, to produce the natural 
disengagement of caloric whenever the patient is 
exposed to a cold and free atmosphere; but in 
health the motion of the blood, its contact with 
the nervous system, and the friction of the 
muscles, are adequate to support the calorific 
process requisite in the animal economy. 
xu. Intense thought, not long continued, 
creates increased temperature of the head; when 
the mental functions are suspended by sleep, the 
temperature generally sinks about one degree. 
Whatever operates powerfully on the nervous 
system, such as violent pain, fear, grief, and 
miasma, causes a reduction of animal temperature ; 
cold may be so intense as to suspend or destroy 
this and all the other functions of the nerves. 
xiv. Some have supposed, and among others 
Mr. Hunter, that the human body possesses a 
frigorific as well as a calorific power; this is 
physically impossible, for two properties, incom- . 
patible with each other, cannot exist in one 
body at the same time. The following is one 
of the experiments on which Mr. Hunter lays 
great stress: “the living and dead parts (two 
penes) being both immersed in water, gradually 
made warmer and warmer from 100° to 118°, and 
