Effort brings about a momentary stoppage of respiration, and in this already we have a hindrance to the functions of the lungs. But there is further an action on the heart and great vessels, through the necessity put on the thoracic organs to serve as points of support for the ribs. To the ribs in fact are attached the powerful muscles which fix the thorax during the execution of movements demanding a great expenditure of force. The lungs, inflated by a forced inspiration, act as a kind of cushion on which the ribs press, and this pressure is transmitted to the great thoracic vessels and to the heart itself.

It is easy to understand the fatigue of the heartmuscle and of the contractile walls of the blood vessels which must result from this mechanical action which quickly and excessively increases the tension in the vascular system.

Every exercise which demands a series of efforts, repeated at short intervals, very quickly induces fatigue of the heart, and diminution of the contractile force of the blood-vessels. There results a transient condition of asystole, and the subject is for some minutes in the condition of a person suffering from cardiac disease. Breathlessness is thus produced by a kind of overdriving of the heart, and by the passive congestion of the lungs which this immediately produces.

On performing an exercise needing very prolonged efforts, breathlessness comes on with astonishing quick

ness.

Two wrestlers who strain, each trying to throw the other, remain for a few seconds completely motionless owing to the resultant of their several efforts which balance each other, then suddenly one of them gives way and yields to the pressure of the other. It has hardly taken half-a-minute, but the two champions are pale, breathless, and unable to speak. For some seconds it seems as if the air can no longer enter their chests. Under the great pressure occasioned by their athletic effort the larger vessels have been distended until they have momentarily lost power of recoil, the heart has

been compressed till it is on the point of ceasing to beat, and the lungs, engorged with blood which is no longer driven forward, remain for a moment under the power of passive congestion, which renders them unable to work.

Effort plays an important part in all movements which are executed with a person's whole force. We must often attribute effort rather to the energy which a man throws into an exercise than to the mechanism of the exercise. Thus long-distance running does not need the production of effort, while this action occurs during sprint running. Hence the latter can only be continued for a very short time without producing breathlessness.

CHAPTER IV.

BREATHLESSNESS—(concluded).

Three Stages of Breathlessness-First or Salutary Stage; Respiration more Active but not Insufficient-Second Stage-Symptoms of slight Carbonic Acid Intoxication; Leaden Complexion; Breathless Respiration; General Discomforts-Third or Asphyxial Stage-Cerebral Disturbances; Symptoms of severe Carbonic Acid Intoxication; Vertigo; Unconscious Movements: Syncope; Stoppage of the Heart-Observations-Dangers of Running as a Sport-Too vigorous an Assault-at-Arms-Animals succumbing to Breathlessness; the Horse ridden to Death-Death of a Carrier Pigeon-A Hunted Beast which Breaks Cover.

WE now know the influence of muscular exercise on the chemical and mechanical phenomena of respiration, and we have studied the effects of work on the circulation of the blood and the movements of the heart. We have thus brought together all the materials which are necessary for establishing the physiology of the very complex general state called breathlessness, and we may sum up its principal features.

The prime cause of breathlessness during exercise, is the excessive production of carbonic acid.

The accessory causes are: (1) the disturbances of the respiratory movements produced by muscular exercise (2) the disturbances in the circulation of the blood, and the congestion of the lungs which these cause.

We have seen how an excess of carbonic acid is produced by the combustions which occur during muscular work. We have seen how everything concurs in favouring its accumulation. We have before us an organism striving against a cause of disorganisation. It remains for us to examine the various incidents in this combat, the manner in which the organism defends itself, the conditions in which it has the upper hand, and the conditions in which it may succumb.

I.

We may group in three stages the symptoms presented by a man whose respiration is under the influence of violent exercise.

In the first stage, the respiratory movements are increased in frequency and in extent. The production of carbonic acid is increased, but the respiratory energy being greater, there is an equilibrium between the needs of the organism which demands a more active elimination of this gas, and the working of the lungs which is powerful enough to satisfy these needs. During a time, which varies much with the individual, with his constitution, with his resistance to fatigue, and above all with his power of directing his respiration, gained from his respiratory education, these are only symptoms of greater vital activity, and there are as yet no signs of functional disturbance, no sensation which rises to the degree of discomfort. The man has a general sensation of warmth, some throbbing of the temples, and has an animated appearance, flushed, his eyes sparkling, and a general aspect of cheerfulness due to the greater activity of the circulation and the resulting active congestions. In a word it is the stage in which exercise causes a greater intensity of life, without reaching the degree of discomfort or of danger.

Here we have the really salutary dose of exercise, the limits within which we must keep in order that work may cause us no inconvenience. But nothing varies more with the individual than the duration of this inoffensive period, which is, in a sense, the preface of breathlessness. In some persons it is as long as an hour; in others the stage in which discomfort begins is reached in a few seconds.

If violent exercise is prolonged, the equilibrium is soon broken between the production of carbonic acid, which becomes more and more abundant, and the eliminating power of the lungs which is insufficient to free the organism from it. Respiratory distress occurs. In the second period, the effects of insufficient respira

tion begin to show themselves, a vague discomfort is experienced, which is most accentuated in the præcordial region, but which is rapidly generalised throughout the body and notably affects the head. In the chest there is a feeling as if it were oppressed by a weight, or bound down by a girdle, of insufficient air. In the head there are clouds obscuring sight, sparks before the eyes, then murmurs and ringing in the ears, and finally a certain bluntness of sensation, a certain confusion in impressions and in ideas. All these disturbances are due to the action upon the nerve-centres of an excess of carbonic acid. They indicate the beginning of intoxication.

In the face remarkable changes are to be noticed, which are the consequences of the respiratory distress and of the efforts made to draw a greater quantity of air into the chest. The nostrils are dilated, the mouth and eyes widely opened. They all seem to be widely opened to favour the entrance of the air which the lungs so greatly need.

In certain animals the movements associated with respiratory effort are especially noticeable in the nostrils. A horse returning to its stable after a race is typically breathless, and we can study in it the to-and-fro movement of the nostrils which accompanies the movement of the flanks.

The alternating movements of elevation and depression of the alæ nasi have for their object the presentment of a large passage to the air drawn into the chest. They tend to occur in every animal with increased respiratory need. When we look at a small child suffering from acute bronchitis or pneumonia, we see a very characteristic working of the nostrils, which at once makes the doctor think of a disease of the respiratory organs.

The colour of a breathless man shows very striking modifications. At the beginning of exercise we have said that there is animation, more colour in the face, due to active congestion. But in the second period the picture has changed. To the lively red colour has succeeded a pale and wan tint. There is something peculiar about this pallor; it is not uniform. Certain parts of