BY DR. BURDON-SANDERSON. 327 



cumstances, the arterial pressure-curve exhibits the undula- 

 tions in question.. It has, however, been lately shown by 

 Hering, that the state of asphyxia is far from being essential, 

 and that the most certain way of producing the phenomenon 

 is to bring the blood of the animal into a state which corre- 

 sponds to dyspnoea, not by stopping the artificial respiration 

 altogether, but by gradually diminishing the quantity injected 

 at each stroke. In the arterial tracings so obtained it is seen 

 that the cardiac intervals are of uniform duration in other 

 words, that there are no variations of pulse-frequency, the vagi 

 having been divided. When these nerves are left intact, curves 

 are obtained (fig. 262 1 ) in which the variations of the pulse 

 intervals exhibit the same relation to those of the arterial 

 tension as in the normal condition the pulse-frequency being 

 greater in the ascending limb of each respiratory wave than 

 in the descending. From this we learn that the variations of 

 frequency are dependent on the integrity of the vagi. The 

 proof that the variations of pressure are vascular in their 

 origin, and depend on corresponding changes of arterial tonus, 

 is shown by two experimental results, viz. : (a) that although 

 after section of the spinal cord, arterial pressure is still sub- 

 ject to variations which are no doubt dependent on changes 

 of arterial tonus, these are very irregular ; and (b) that the 

 rhythmical variations of pressure persist after the influence of 

 the heart has been eliminated. The latter fact has been de- 

 monstrated by Hering, who has shown that if circulation is 

 maintained artificially, independently of the heart, in an ani- 

 mal which is placed in other respects in conditions favorable 

 to the production of u Traube's curves," they exhibit them- 

 selves with the same distinctness as when the heart is in action. 

 The conclusion to be derived from the preceding experiments 

 may be expressed as follows: The rhythmical variations of 

 arterial pressure which are associated with the respiratory 

 movements, are dependent on corresponding variations of 

 arterial tonus, but the variations of the frequency of the con- 

 traction of the heart are governed by the inhibitory nervous 

 system of that organ. In accepting this proposition, it must 

 not be forgotten that under normal conditions the thoracic 



1 The tracings, fig. 262, are those of a curarized dog with undivided 

 vagi, in which air is injected into the lungs at regular intervals, but in 

 insufficient quantity. Tke arterial curve differs from "Taube's" only 

 in this respect that in the ascending limb of each wave, the wavelets 

 which express the arterial pulsations are more frequent than in the 

 descending. In the lower tracing the ascents mark the strokes of the 

 artificial respiration apparatus, which was working at intervals of five 

 seconds ; the variations of arterial pressure shown in the upper tracing 

 follow the rhythm of the natural respiratory movements, and conse- 

 quently do not correspond with the inflations. 



