154i - REPORT — 1873. 



tliose diseaseg ■wliicli arise within tlie body from ordinary changes in the environ- 

 ment ; and this is equally true of the other zymotic diseases. On the other Iiand 

 it might easily be shown that they have very little affinity with the true parasitic 

 diseases. All these considerations tend to show that the germ- theory is inapplicable 

 to the zymotic diseases. 



The Cause of the Respiratory Variations of Arterial Pressure. By Dr. Bcr- 

 DON Sanderson, F.R.S., Professor of Practical Physiology, University Col- 

 lege, London. 



The purpose of this paper was to show experimentally that the rhythmical 

 variations of arterial pressure, and of the frequency of the contractions of the heart, 

 which are normally associated with the respiratory movements, ma}' occur in the 

 absence of those movements, and that they cannot therefore be whollj' dependent 

 upon them. This is proved hy the observation that in animals which are gradually 

 subjected to the toxic action of curare while the variations of arterial pressure and 

 pulse-rate are continuously recorded on the kymograph, these variations persist 

 after the respiratory movements have ceased. 



The experimental results which form the subject of this communication were 

 obtaiucftl by the author in the year 18G7. They are now published for the first time, 

 by way of supplement to certain recently published observations of Prof. Hering 

 on the subject. 



The normal relation between the curve of arterial pressure and that of thoracic 

 expansion and contraction is now well known. In the dog each inspiratory act is 

 followed by an increase of arterial pressure with acceleration of the frequency of 

 the contractions of the heart. During the period of expiration, i. c. the interval 

 which separates one inspiration from its successor, the arterial pressure sinks and 

 the pulse becomes much less frequent. In both cases the phenomena relating to 

 the circulation always occur later than the corresponding respirator}' movements ; 

 so that, c. ff., the period of increase of arterial pressure and pulse-frequency always 

 begins and ends later than inspiration, coinciding usually in tbe dog with the latter 

 half or two thirds of the inspiratory act and the beginning of the act of expiration. 

 Hence the interval between each such period and its successor coincides with the 

 latter part of tbe expiratory period and the beginning of inspiration, i. e. begins a 

 little after each expiration and lasts after the beginning of each inspiration. In a 

 dog previously narcotized by morphia it is possible, by employing a very small dose 

 of curare, to arrest the respiratory movements by such slow degrees that the eilect 

 of their gradual cessation on the variations of arterial pressure maj' be watched in 

 all its stages. For this purpose it is necessary before injecting the curare to connect 

 the carotid or crural artery of the animal with the manometer of the kymograph, 

 and to record the respiratory movements simultaneously on the same cylinder in 

 such a way that the two tracings may be written one above the other, and that 

 their synchronous points may be always in the same vertical line. Tracings so 

 obtained corresponding to various stages in the action of the curare were exhibited. 

 The lirst showed the character of the arterial and respiratory curves, and their 

 relation to each other before any curare had been given. The second exhibited the 

 state of the circulation when the respiratory movements, although irregular, were 

 still vigorous. At the third period the respiratory movements had become very 

 shallow, and there was a distinct interv.al between inspiration and expiration : the 

 inspiratory eftbrt was then attended with a slight twitching of the external muscles 

 of the larynx, and expiration with a similar twitching of certain muscles of the limbs. 

 Finally, in the last tracing of the series it was seen that, although the eftect of the 

 expiratory effort was no longer perceptible, there was a slight jerk downwards of the 

 lever which represented inspiration. 



Corresponding to these successive diminutions of respiratory movements, it was 

 seen that the variations of arterial pressure, although they diminished, did not dis- 

 appear. _ Throughout the whole period of observation it was observed not only that 

 the variations of pressure and pulse-rate continued, but that they preserved the 

 same relation precisely to the slight movements which represented inspiration and 



