ITS SCOPE AND METHOD 75 



and I have a sensation of warmth from it, that is good 

 proof that a nerve a so-called sensory nerve runs 

 from the skin there to my nerve-centres and that these 

 are connected with my brain. 



A region of skin, the nerve-fibres of which have been 

 severed, does not flush with blood properly when ex- 

 posed to warmth, nor does it become moist with perspira- 

 tion. Therefore the course of events in the regulative 

 mechanism is that the heat playing on the skin stimulates 

 nerves that run to the nerve-centres, and that these in 

 turn stimulate nerves which run thence to the blood- 

 vessels and the glands. In fact the mechanism includes 

 nervous reflex action. 



Thus in our problem of the warmth of the body nerves 

 are involved. I have spoken rather glibly about nerves, 

 but our knowledge of them is meagre, especially as to 

 how they work. Chemistry is here at a disadvantage, 

 for its difficulties are enhanced by the minuteness of the 

 quantity of material disbursed by nerves ; the turn-over 

 of material in them is relatively small. 



The smallness of the turn-over of energy and material 

 in the nerves depends largely on the fact that, spread 

 like a delicate network through the body and furnishing 

 as it were telephonic communication between the various 

 organs and regions, their reactions act like releasing 

 forces, themselves small though controlling machinery 

 in which large quantities of force may run. A tele- 

 phonic message expends little energy, but it may set 

 a train in motion or stop the marching of an army corps. 

 Suppose we knew nothing of the mode of action of tele- 

 phones and knew concerning a telephonic system only its 

 places of departure and its end-results at various stations. 

 That would represent the position of physiology in 

 regard to most of its observations on the nervous system 



