516 Dynamic Theory. 



ing the heart, the blood and tissues must be in contact with oxygen and 

 be burnt up by it. So, a detached frogs heart, which in a vacuum 

 would beat 20 to 30 minutes, would in pure oxygen beat twelve hours ; 

 but in carbonic acid it would beat only ten minutes, and in chlorine gas 

 only two. 



The heart, like other muscles, is supplied with the polar energy neces- 

 sary to cause its contractions by the oxidization of its own tissues and 

 blood as the above cited facts abundantly prove. It differs from most 

 muscles in the fact that its contractions are in general rythmical and 

 continuous, while theirs are occasional, incidental and conditional. The 

 muscles concerned in respiration are like the heart, ordinarily rythmical 

 in their action, but may be interfered with and disturbed within narrow 

 limits. The movements of the muscles concerned in digestion are con- 

 ditional and casual, and ordinarily get their start from the contact and 

 pressure of the food, and the force necessary to keep them up comes 

 from the conversion of the chemical energy of digestion into electrical 

 energy. Their activities are said to be automatic, and so are the activi- 

 ties of the neart and respiratory organs. 



The heart is automatic to the extent that the force which causes its 

 ordinary contractions is generated within it. The blood is thrown into 

 the heart by way of the coronary arteries, and it is the consumption of 

 the materials supplied by this blood that furnishes the motive power for 

 the contractions of the heart. But it is these contractions which force 

 the blood into the coronary arteries ; so that each contraction makes 

 provision for the next, and hence the perpetual rythm. There is con- 

 siderable rythm in the movements of the intestines, which is kept up 

 during the presence of the food products, but when these are consumed, 

 the movement stops. But the heart does not stop, because the blood is 

 never consumed. The force furnished by the blood delivered to the 

 heart by the coronary arteries, is very much more than enough to run 

 the heart alone. This is seen in the case of the frog's heart detached 

 from the body, and so deprived of the blood supply. It then runs by 

 force obtained by the consumption of its own tissues and the small 

 amount of blood in them. But it runs light like an empty wagon. In 

 the body it not only moves itself but propels a great load of blood to all 

 parts of the system. The blood which is thus sent off to the other 

 parts of the body, generates in them an amount of force proportional to 

 that furnished to the heart by the coronal blood. This force is of a 

 definite average amount in each individual ; and it depends primarily on 

 the size and organization of the individual, and secondarily, on the fre- 

 quency and energy of the stimulations to which he is subjected from 

 without. It is never enough to run all parts of the body up to their 

 highest capacity at the same time, so that when there is call for a spe- 



