The embarrassment of respiration and the pressure of the air in the distended alveolæ by impeding the capillary circulation of the lungs prevent the left auricle from receiving its full supply of blood; hence the pulse is small and weak during the paroxysm, but regains its natural volume as soon as its immediate effects are over. The action of the heart, like every other phenomenon of asthma, is subject to constant variation. At one moment it beats tumultuously, while at the next its action may be so feeble as to cause temporary syncope (Sée). The venous blood, unable to overcome the obstacles to its passage, is forced back into the vessels, causing distension of the cervical veins and the jugular pulse sometimes observed in severe attacks. The bluish hue of the face in bad cases is due to cyanosis resulting from insufficient aëration of the blood. The paroxysm is unattended with fever, the temperature, if altered at all, being rather below than above the normal. Coldness of the face and hands is quite a common symptom in protracted cases. In addition to the nervous sensations described among the premonitory symptoms, patients have been known to suffer from disturbances of a more {189} serious nature during the paroxysm. In some instances there is complete loss of consciousness, and Riegel[7] states that such cases have been known to have tetanic convulsions of the trunk and extremities. [Footnote 7: _Loc. cit._ p. 285.] The course of an attack of asthma is in most cases quite typical, the paroxysms recurring nightly for an indefinite period, and usually increasing in severity until, as in epilepsy and other nervous diseases, it finally exhausts itself. On awaking from the sleep which usually succeeds the final paroxysm the patient, unless the attack has been very mild and of short duration, feels weak and exhausted, but there is no tendency to the recurrence of the dyspnoea; on the contrary, he may expose himself with perfect impunity to the causes which at other times would be certain to produce an attack. The chest feels stiff and sore, the cough and expectoration diminish, and in a few days disappear, and if the disease has produced no organic lesion the patient returns to his usual state of health. DURATION.--The duration of asthma, except in young persons and in those rare cases in which the cause can be discovered and removed, is very indefinite, the disease lasting for years, if not for life. As the patient grows older the attacks become less severe, but are more frequent. Sometimes a case which has recurred for years and defied the most energetic treatment will all at once recover of itself. SEQUELÆ.--Although bronchial asthma is essentially a neurosis, and therefore purely functional in its character, it is rare for it to continue for any great length of time without causing some organic affection of the lungs or heart.