*[Footnote: The excessive production of heat in muscular work gives rise to sweating. The evaporation of sweat helps to keep the body temperature from rising unduly from the heat of exertion. Again in strong emotion and in pain the “cold sweat” that appears on the skin may be regarded as a reaction anticipatory of the strenuous muscular movements that are likely to ensue.] As the air moves to and fro in the lungs with each respiration, it must pass through the fine divisions of the air tubes or bronchioles. The bronchioles are provided with smooth muscle, which, in all probability, like smooth muscle elsewhere in the body, is normally held in a state of tonic contraction. When this tonic contraction is much increased, as in asthma, breathing becomes difficult, and even with the body at rest unusual effort is then required to maintain the minimal necessary ventilation of the lungs. During strenuous exertion, with each breath the air must rush through the bronchioles in greatly increased volume and speed. Thus in a well person “winded” with running, for example, the bronchioles might become _relatively_ too small for the stream of air, just as they are too small in a person ill with asthma. And then some extra energy would have to be expended to force the air back and forth with sufficient rapidity to satisfy the bodily needs. It is probable that even under the most favorable conditions, the labored breathing in hard exercise involves to some degree the work of accelerating the tidal flow of the respiratory gases. This extra labor would obviously be reduced, if the tonic contraction of the ring-muscles in the wall of the bronchioles was reduced, so that the tubules were enlarged. It has been shown by a number of investigators, who have used various methods, that adrenin injected into the blood stream has as one of its precise actions the dilating of the bronchioles.[148] The adrenin discharged in emotional excitement goes to the lungs before entering into relation with any other organ except the right heart chamber; it may, therefore, have as its first effect the relaxation of the smooth muscles of the lungs. This would be another very direct means of rendering the organism more efficient when fierce struggle calls for a bounteous supply of fresh air and a speedy discharge of the carbonaceous waste. Effects Produced in Asphyxia Similar to Those Produced in Pain and Excitement All the bodily responses occurring in pain and emotional excitement have thus far been considered as _anticipatory_ of the instinctive acts which naturally follow. And as we have seen, these responses can reasonably be interpreted as preparatory to the great exertions which may be demanded of the organism. This interpretation of the facts is supported by the discovery that a mechanism exists whereby the changes initiated in an anticipatory manner by emotional excitement are continued or perhaps augmented by the exertion itself.