igoo-i.] Observations on Blood Pressure. 203 



In Tracing 20 another illustration of the same thing occurs. At S, 

 the animal, which was not at all under the influence of an anaesthetic, 

 began to struggle violently, and the result was a rise in pressure, with 

 quickening of the pulse. At i chloroform was started and pushed. 

 The pressure began to fall quickly at 2 with great hastening of the 

 pulse. At 3 chloroform was stopped, as the slowing of the pulse 

 heralded threatened respiratory failure, but at 4 the respiration did 

 cease, with the usual great slowing of pulse and fall of blood pressure. 

 The animal eventually recovered under artificial respiration. This 

 extreme and sudden fall of the blood pressure occurring synchronously 

 with the stoppage of the respiration was noted by the first Hyderabad 

 Commission, who stated the case as follows. " Although a gradual loss 

 of tension in the arteries took place after the first stage, the decrease of 

 tension was more abrupt when the respiration became affected. The 

 stoppage of the respiration was always succeeded by a sudden increase 

 in the relaxation of the coats of the femoral artery and a fall in tension." 

 It is difficult, however, to understand how they could have concluded 

 that, " It was further observed that struggling demanded that the 

 chloroform be pushed and not withheld." No advice could well have 

 been more dangerous than this, and fortunately the second Hyderabad 

 Commission put it right. The chart just given shows that struggling 

 raises the pressure, and that if chloroform be commenced during the 

 struggling, then the pressure falls almost at once, in fact, it seems from 

 what we have observed that the preliminary rise in blood pressure in 

 chloroform anaesthesia is not due to any vaso-motor stimulation, but 

 rather to the almost constant slight struggling — it may be only increased 

 breathing — which occurs then. Dr. J. A. McWilliam' found that 

 " with moderate respiration the results of a certain dose of chloroform 

 were very slight, whereas the same dose during exaggerated respiration 

 caused great depression and extensive fall of blood pressure." 



While all admit that a considerable dose of chloroform produces a 

 great fall in blood pressure, it is not settled how it does so. Many 

 believe that it is due to the paralysing action of the drug on the vaso- 

 motor centre,'- while on the other hand, Shore and Gaskell's cross 

 circulation experiments seem to prove that it is due to the direct action 

 of chloroform on the heart. These cross circulation experiments, 

 however, involve a very difficult technique, and when repeated by others 

 have not always given the same results.^ 



1 British Medical Journal, Oct. 1890. 



2 Journal of Physiology, Vol. XXI., Nos. 4 and 5, 1897. 



.5 "Cross Circulation Experiments," Lieut. -Col. Lawrie, Lancet, i8q8. Vol. II. p. 24. 



