The annulling of pain, and, in some cases, its complete annihilation, can be accomplished in many ways. Narcotics, anaesthetics--local and internal--direct action of cold, and mesmeric or physiological influence, have all their advocates, and each _will surely_ do its work. There is one thing about which, I think, we can all agree, as to these agencies; unless the _will_ is partially and in some cases completely subjugated there can be no primary or secondary effect. The voluntary muscles must become wholly or partially paralyzed for the time. Telegraphic communication must be cut off from the brain, that there be no reflex action. It is not necessary there should be separate nerves to convey pleasure and pain any more than there should be two telegraphic wires to convey two messages. If, then, we are certain of this, it matters little as to whether it was done by corpuscular poisoning and anaemia as from chloroform or hyperaemia from ether. I think we are now prepared to show clearly the causes which effect the phenomena in "rapid breathing." The first thing enlisted is the _diversion of the will force_ in the act of forced respiration at a moment when the heart and lungs have been in normal reciprocal action (20 respirations to 80 pulsations), which act could not be made and carried up to 100 respirations per minute without such concentrated effort that ordinary pain could make no impression upon the brain while this abstraction is kept up. Second. There is a specific effect resulting from enforced respiration of 100 to the minute, due to the _excess of carbonic acid gas set free from the tissues_, generated by this enforced normal act of throwing into the lungs _five times_ the normal amount of oxygen in one minute demanded, when the heart has not been aroused to exalted action, which comes from violent exercise in running or where one is suddenly startled, which excess of carbonic acid cannot escape in the same ratio from the lungs, since the heart does not respond to the proportionate overaction of the lungs. Third.--Hyperaemia is the last in this chain of effects, which is due to the excessive amount of air passing into the lungs preventing but little more than the normal quantity of blood from passing from the heart into the arterial circulation, but draws it up in the brain with its excess of carbonic acid gas to act also directly upon the brain as well as throughout the capillary and venous system, and as well upon the heart, the same as if it were suspended in that gas outside the body. These are evident to the senses of any liberal observer who can witness a subject rapidly breathing.