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body, where there is no microscopical ganglion, and where these 

 parts have ceased to be under the influence of the nervous centres. 



The three theories which I have examined being unable to ex- 

 plain the beatings of the heart, I will now expose my theory, 

 and discuss the three following questions : 1. What is the exci- 

 tant which puts the heart in action ? 2. Does that excitant act 

 rhythmically ? 3. Does that excitant act together directly on 

 the muscular fibres of the heart, and on the nervous system ; or 

 does it act only on the muscular fibres ? 



After having solved these three questions, I will examine the 

 objections which might be made to the doctrine I propose. 



1. What is the excitant which puts the heart in action ? 



I believe that the beatings of the heart are excited by a prin- 

 ciple existing in the blood, and that carbonic acid is that princi- 

 ple. This view is grounded on the following facts : 



a. When we prevent a warm -blooded animal from breathing, the 

 beatings of the heart become more frequent than before, for about 

 one or two minutes. It is not on account of the emotion alone 

 that it is so, because the same effect is produced when we as- 

 phyxiate suddenly an animal which has entirely lost his power 

 of having emotions, in consequence of the action of chloroform. 



b. Many times I have found, on myself and on one of my 

 friends, that the beatings of the heart are rendered more active 

 during asphyxia. We hold our breath for about three quar- 

 ters of a minute, and during the last fifteen seconds the heart 

 beats from two to four (in one case five) minutes more than when 

 the respiration was free. We have made the experiment in the 

 sitting position, avoiding any movement of the body in all the 

 cases. 



c. John Reid has discovered that when any hemadynamometer is 

 put in the femoral artery of a dog, the mercury rises in the in- 

 strument if the animal is asphyxiated, and about one minute after 

 the respiration has been stopped. The same result has been ob- 

 tained in twenty experiments. It seems to me that this fact 

 proves that the contractions of the heart become more energetic 

 during asphyxia. John Reid attributes the result he has obtained 

 to some difficulty that black blood seems to have in passing through 

 the capillaries of the different parts of the body. I do not deny 

 that there is such a difficulty ; but I think that the great reason 



