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Sneezing, for example, is a specific response made by the motor mechanism to stimulation of nociceptors in the nose, while stimulation of the larynx does not produce a sneeze, but a cough; stimulation of the nociceptors of the stomach does not produce cough, but vomiting; stimulation of the nociceptors of the intestine does not produce vomiting, but increased peristaltic action.
Each discharge of energy is subtracted from the sum total of stored energy and, whether the subtractions are made by the excitation of nociceptors by trauma, by tickling, by fighting, by fear, by flight, or by the excitation of sexual receptors, by any of these singly or in combination with others, the sum total of the expenditure of energy, if large enough, produces exhaustion.
As a further remarkable proof of the marvelous adaptation of the body mechanism to meet varying environmental conditions, we find that just as nociceptors have been implanted in only those parts of the body which have been subject to nocuous contacts, so a type of infection which causes muscular action in one part of the body may cause none when it attacks another.
As we have shown, the bene- and nociceptors orientate man to all forms of physical contact the former GUIDE HIM TO the acquisition of food and to sexual contact; the latter DIRECT HIM FROM contacts of a harmful nature.
Observations on Patients whose Associational Centers are Dulled, and on Diseases and Injuries of Regions not Endowed with Nociceptors Reversing the order of our reasoning, let us now glance at the patient who is unconscious and who, therefore, has lost much of the power of association.
There should be no more difficulty in evolving an efficient army of phagocytes by natural selection, or in developing specific chemical reactions against *microscopic enemies, than there was in evolving the various nociceptors for our nerve-muscular defense against our *gross enemies.
By the law of phylogenetic association, we are now prepared to make a practical application of the principles of the discharge of nervous energy. Under such conditions the nervous system is protected against noci-association, resulting from noci-perception or from an adequate stimulation of nociceptors.
The brain, therefore, contains no mechanism no nociceptors the direct stimulation of which can cause a discharge of nervous energy in a self-defensive action. That is to say, direct injury of the brain can cause no purposeful nerve-muscular action, while direct injury of the finger does cause purposeful nerve-muscular action.
On these premises we should conclude that the turtle, the armadillo, and the skunk have fewer nociceptors than has a dog or man, and that they would show less response to trauma. It was indeed relatively difficult to exhaust the skunks and armadillos by trauma. These experiments are too few to be conclusive, but they are of some value and furnish an excellent lead.
Adequate stimulation of the nociceptors for pain is not the only means by which a discharge of nervous energy is caused. Nervous energy may be discharged also by adequate stimulation of the various ticklish regions of the body; the entire skin surface of the body contains delicate ticklish receptors.
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