CH. XXIV.] 



TRAUBE-HERING CURVES. 



367 



muscles are violently contracted, as in extraordinary expiration, 

 the same effect will be produced as by inspiration. The effect 

 of the varying intra-thoracic pressure which occurs during inspira- 

 tion upon the pulmonary vessels is to produce an initial dilatation of 



Fig. 328. Traube-Hering's curve*. (To be mid from left to right.) The curves i, 2, 3, 4 

 and 5 are portions selected from one continuous tracing forming the record of a pro- 

 longed observation, no that the several curves represent successive stages of the same 

 experiment. Each curve is placed in its proper position relative to the base line, which 

 is omitted ; the blood-pressure rises in stages from i to 2, 3, and 4, but falls again in 

 stage 5. Curve i is taken from a period when artificial respiration was being kept up, 

 but the vagi having been divided, the pulsations on the ascent and descent of the undu- 

 lations do not differ : when artificial respiration ceased these undulations for a while 

 disappeared, and the blood-pressure rose steadily while the heart-beats became slower. 

 Soon, as at 2, new undulations appeared ; a little later, the blood-pressure was still 

 rising, the heart-beats still slower, but the undulations still more obvious (3) ; still 

 litter (4), the pressure was still higher, but the heart-beats were quicker, and the 

 undulations flatter, the pressure then began to fall rapidly (5), and continued to fall 

 until some time after artificial respiration was resumed. (M. Foster.) 



both artery and veins, and this delays for a short time the passage 

 of blood towards the left side of the heart, and the arterial pressure 

 falls, but the fall of blood-pressure is soon followed by a steady 

 rise, since the flow is increased by the initial dilatation of the 

 vessels : the converse is the case with expiration. As, however, 

 the pulmonary veins and capillaries are more easily dilatable than 



