624 VASCULAR SYSTEM IN ASPHYXIA. [BOOK n. 



fact that the vaso-inotor nervous system is apt to fall into a 

 condition of rhythmic activity. It has been suggested that the 

 normal respiratory undulations may be due to a rhythmic rise and 

 fall of the activity of the vaso-motor centre, synchronous, like that 

 of the cardio-inhibitory centre, with the respiratory movements. 



FIG. 87. BLOOD-PRESSURE CURVE OF A BABBIT, RECORDED ON A SLOWLY MOVING 



SURFACE, TO SHEW TRAUBE-HERING CURVES. 



(The curve was described not by means of a mercury manometer, but by an 

 instrument similar to but not identical with Pick's spring-kymograph.) In each 

 heart-beat the upward and downward stroke are very close together but may be 

 easily distinguished by the help of a lens. The undulations of the next order 

 are those of respiration. The wider sweeps are the Traube-Hering curves, of 

 which two complete curves and portions of two others are shewn. Each Traube- 

 Hering curve comprises about nine respiratory curves, and each respiratory curve 

 about the same number of heart-beats. 



There can however be no doubt that the respiratory variations 

 in blood-pressure are due to the mechanical conditions discussed 

 above, and that vaso-motor influences intervene but little if 

 at all. 



388. The further general effects, similar to the above, on 

 the vascular system of deficient arterialization of the blood may be 

 studied by taking a blood-pressure tracing from the carotid or 

 other artery of an animal while the interference with respiration 

 is pushed on to a fatal asphyxia. During the first and second 

 stages of the asphyxia the blood-pressure rises rapidly, attaining 

 a height far above the normal. During the third stage it falls 

 even more rapidly, repassing the normal and becoming nil as 

 death ensues. If the animal, no urari having been given, is 

 breathing of itself, and if, as usually is the case, the asphyxia is 

 brought about by occlusion of the trachea, so that the mechanical 

 effects of the respiratory movements are exaggerated by the air 

 being unable to enter the chest, the respiratory undulations of 

 the pressure-curve due to the mechanical causes discussed above 

 are, especially during the first stage, extensive, abrupt and 

 irregular, the inspiratory movements being accompanied by a 

 conspicuous fall of pressure. When the animal has been pre- 



