406 OF RESPIRATION. 



an hour had intervened between birth and the employment of resuscitating 

 means, and when probably a much longer time had elapsed from the period 

 of the suspension of the circulation. 



324. The phenomena presented in Asphyxia, 1 whether produced by sud- 

 denly cutting off the supply of air, or more slowly by permitting the animal 

 to breathe through a narrow chink, are very similar, though in the latter 

 case, the successive stages can be more easily followed. In the first instance 

 there are violent iuspiratory, followed after a short time by equally violent 

 expiratory efforts, which culminate in convulsions, the abdominal and other 

 expiratory muscles being those chiefly affected. When the access of air to 

 the lungs has been suddenly prevented, the expiratory convulsions with 

 spasms of the muscles of the limbs occur within the first minute, and are so 

 marked and peculiar as to have been attributed to the excitation of an expi- 

 ratory convulsive centre. During this period the tension of the blood in the 

 vessels is greatly increased. After the convulsions have lasted a few seconds 

 they often cease suddenly, and are followed by a period of calm. The expi- 

 ratory movements cease, efforts to inspire occur with long but tolerably regu- 

 lar intervals between them, and at each effort, when the occlusion of the 

 trachea has been sudden, the blood-pressure falls, so that at the end of the 

 second minute it is considerably less than natural; when, however, Asphyxia 

 has been slowly produced, the blood-pressure as well as the frequency of the 

 heart's beats continue to increase during this period. Reflex movements 

 now cease, and the pupil becomes widely dilated and insensible to light. In 

 suddenly produced and complete Asphyxia death ensues in the course of 

 three or four minutes, preceded by inspiratory movements which are slow, 

 feeble, and irregular, two or three efforts being made successively, followed 

 by a long pause. In the spasms which accompany the final gasps the head 

 is thrown back, the trunk is straightened or arched backward, and the limbs 

 are extended, whilst the mouth gapes, and the nostrils dilate. These so- 

 called stretching convulsions are of quite a different type from the previously 

 mentioned expiratory convulsions. The augmentation of the blood-pressure 

 which occurs during the first period of Asphyxia, is occasioned by the circu- 

 lation of non-arterialized blood through the vaso-motor centre, the excitation 

 of which causes contraction of the smaller arteries. The effect of this con- 

 traction is to fill the venous system, which becomes still more distended by 

 the obstacle to the onward movement of the blood, presented by the con- 

 traction of the expiratory muscles of the trunk and extremities. The heart 

 being abundantly supplied with blood, fills rapidly during diastole and con-" 

 tracts vigorously, in consequence of which, and of the increased resistance 

 in front, the arterial pressure rises. This last effect is, however, temporary: 

 the diastolic intervals being lengthened by the excitation of the inhibitory 

 nervous system, and the heart itself weakened by defect of oxygen, the organ 

 soon passes into a state of diastolic relaxation. Its contractions become 

 more and more ineffectual till they finally cease, leaving the arteries empty, 

 the veins distended, and its own cavities relaxed and full of blood. The 

 heart's contractility is not finally lost, however, nearly as soon as its move- 

 ments cease; for the action of the right ventricle may be renewed, for some 

 time after it has stopped, by withdrawing a portion of its contents either 

 through the pulmonary artery, their natural channel or, more directly, by 

 an opening made in its own parietes, in the auricle, or in the jugular veiu 

 ($ -.'>7). On the other hand, the left ventricle may be again set in action, 



1 See Biirdon-Sanderson in the Handbook for the Physiological Laboratory, 1873, 

 p. 319 et seq. 



