446 Experiments with Pressure on Excitable Tissues. [May 27, 



V. " Experiments with Pressure on Excitable Tissues." By 

 George J. Romanes, F.R.S. Received May 18, 1886. 



The effects of temperature on excitable tissues have been well 

 worked out ; but, so far as I have been able to ascertain, no physio- 

 logist has tried the effects of pressure. From physical analogies it 

 appeared to me probable that increase of pressure would act on 

 excitable tissues in a manner analogous to decrease of temperature, 

 and conversely ; but the results of my experiments have not borne out 

 this anticipation. Nevertheless, the research seems worth publishing. 



In a small glass chamber, made for the purpose, I was able to place 

 the freshly excised heart of a frog or a tortoise, and there to submit 

 the rhythmically beating tissue to any increase of atmospheric 

 pressure that I desired, up to a maximum limit of twenty-two atmo- 

 spheres, beyond which it was not safe to go with the glass chamber 

 that I had. Through one end of this chamber two platinum electrodes 

 were admitted, by means of which I was able to stimulate the nerve 

 of a nerve-muscle preparation, when this, instead of a heart, was 

 placed in the chamber. 



The result of a number of experiments was to show that neither the 

 rhythm of the beating heart nor the excitability of the motor nerve 

 was in any way affected by an increase of twenty-two atmospheres ; 

 for both the rhythm and the excitability remained the same whether 

 the chamber was exhausted by means of an air-pump or filled with air 

 at a pressure of twenty-two atmospheres. In these experiments the 

 excitability of the nerve was tested from time to time by noting the 

 distance from the primary coil to which the secondary coil of an 

 ordinary du Bois induction apparatus had to be drawn in order to 

 yield a minimal stimulation ; and the rhythm of the heart was 

 counted by watching it through the glass. In some of the experi- 

 ments the pressure was let in gradually, in others suddenly ; in some 

 it was let in and again released a number of times in rapid succession ; 

 while in others it was allowed to remain at twenty-two atmospheres 

 without alteration for half an hour. During these long exposures the 

 rhythm of the heart and the excitability of the nerve would sometimes 

 slightly and continuously fall ; but it did not appear to me that this 

 was due to the pressure, since the diminution of excitability in either 

 case was not any greater than that which is often observable in moist 

 chambers at ordinary pressures. 



Wishing to try whether still higher pressures would produce any 

 effects, I discarded the glass chamber and had one made for me of 

 gun-metal. With this I was able to go up to 150 atmospheres, but 

 was not able to see what was going on inside. My method of 



