622 DEFICIENT ARTERIALIZATION. [BOOK n. 



in such a way as to bring about an augmentation of the cardiac 

 stroke rather than a quickening of the rhythm ; but this has 

 not been definitely proved. In any case a slow beat, with such 

 a maintenance of the strength of the cardiac strokes as permits 

 the continuance for some considerable time of a high blood- 

 pressure, is met when the arterialization of the blood is interfered 

 with. Sooner or later, however, the deficiency of oxygen in the 

 blood diminishes the store of explosive compounds in the cardiac 

 muscular substance, the beats lessen in force, often shewing a 

 temporary increase in frequency, and soon become irregular. 



387. The effects of deficient arterialization on the vaso- 

 motor system are well shewn when in an animal placed under a 

 moderate dose of urari so as to eliminate the complications due to 

 contractions of the skeletal muscles, with both vagi divided so 

 as to ensure the elimination of inhibitory impulses from the 

 medulla, artificial respiration is suspended. Soon after the re- 

 spiration is stopped, a very large but steady rise of pressure is 

 observed. See Fig. 86. The rise so witnessed is very similar to 

 that brought about by powerfully stimulating a number of vaso- 

 constrictor nerves ; and there can be no doubt that it is due to 

 the venous blood stimulating the vaso-motor centre in the medulla, 

 and thus causing constriction of the small arteries of the body, 

 especially those of the splanchnic area, since as we shall see, in 

 speaking of the skin, a too venous blood leads to a widening of 

 the cutaneous arteries. We say ' stimulating the medullary vaso- 

 motor centre,' because, though we must admit that, since a rise 

 of pressure follows upon dyspnoea when the spinal cord has been 

 previously divided below the medulla, the venous blood may 

 stimulate other vaso-motor centres in the spinal cord and possibly 

 even act directly on local peripheral mechanisms, yet the fact that 

 the rise of pressure is much less under these circumstances shews 

 that the medullary centre plays the chief part. As we have 

 just said, the effect of this vaso-constriction in raising the pressure, 

 if not assisted by an increase, at all events, is not neutralized by 

 an adequate decrease of the cardiac stroke. Upon the cessation 

 of the artificial respiration, the respiratory undulations of 

 course cease also, so that the blood-pressure curve rises at first 

 steadily in almost a straight line broken only by the heart-beats ; 

 yet after a while new undulations, the so-called Traube or 

 Traube-Hering curves, make their appearance (Fig. 85. 2, 3), 

 very similar to the previous ones, except that their curves are 

 larger and of a more sweeping character. These new undula- 

 tions, since they appear in the absence of all thoracic or pulmonary 

 movements, passive or active, and are witnessed even when both 

 vagi are cut, must be of vaso-motorial origin ; the rhythmic rise 

 must be due to a rhythmic constriction of the small arteries, and 

 this probably is caused by a rhythmic discharge from vaso-motor 

 centres, and especially from the medullary vaso-motor centre. The 



