Electromotive Pheiiom. of the Mammal. Heart. 279 



must look upon it as iudicatiug that the excitatory state at the base 

 lasts longer than at the apex. 



The total dimition of the electrical change in man as measured 

 on the photograph of the plate, is about 0.35"; in the dog, rather 

 less, about 0.30". The numbers given by Landois fur man^) are 



Mean duration of ventricular contraction 192" 



Mean duration of maintenance of contraction 082" 



Mean duration from l)eginning of relaxation to clos- 

 ure of semilimar valves 072" 



Mean duration from closure of semilunar valves to 



beginning of pause 200" 



Total 0.546" 



If we take the first three together as indicating systole of ven- 

 tricle, as Donders does, the number is 0.346", v^hich agrees very closely 

 with our numbers. 



It will be observed on measurement, that the distance of the di- 

 crotic wave in the carotid pulse of fig, 23 from the beginning of the 

 beat is equal to that of the culmination of the third phase from the 

 beginning of the electrical change, that is, according to our interpre- 

 tation it occurs at the time when the excitatory state at the apex 

 ceases. 



The rate of transmission, as Sanderson and Page have shewn, can 

 be measured by the time from the commencement to the culmination 

 of the initial phase; this is too short in our curves to be measured 

 with accuracy, but it appears to be about 0.02", which gives a velo- 

 city of 5 metres per second, assuming the length of the ventricle to 

 be traversed as 10 centimetres. 



It is worthy of note that the direction of the electrical change 

 of the heart beating slowly and normally, is considerably greater 

 than that of the dog's heart, beating 3 times per second under arti- 

 ficial excitation from auricle. If we compare fig. 23 Plate XVII (the 

 heart of man) with fig. 19 Plate XVI we notice the similarity of the 



^) Centralblatt f. d. medic. Wissensch. 1866. p. 179. 



