8o8 



ELECTRO-PH YSIOLOG Y 



Fig. 299. Electro-Cardiograms from Man 

 (Capillary Electrometer) (Einthoven and 

 Lint). Obtained from the same individual 

 at rest (upper curve), and immediately after 

 vigorous muscular exercise (lower curve). 

 The elevations A, C, D, indicate negativity 

 of base to apex ; the notches B and C lf nega- 

 tivity of apex to base. 



potential at this time between its various parts. The T-wave he 

 considers to be produced, when it is present, merely because the 



excitated state does not dis- 

 appear simultaneously over 

 the whole ventricle. 



In the ventricle of the 

 frog and tortoise the same 

 order of development of the 

 negative change is seen, the 

 base first becoming rela- 

 tively negative, then the 

 apex, and then the neigh- 

 bourhood of the origin of 

 the aorta (Fig. 298). 



Under certain conditions 

 the action current of the heart 

 may stimulate the phrenic 

 nerves, causing the dia- 

 phragm to contract synchro- 

 nously with the heart. 



The Human Electro-Cardi- 

 ogram. An electrical change 



accompanies each beat of the human heart. Waller first showed how 

 this may be demonstrated by means of the capillary electrometer. 



Einthoven and 

 Lint then investi- 

 gated the pheno- 

 menon on a large 

 number of persons. 

 From the photo- 

 graphic records of 

 the movements of 

 the meniscus they 

 constructed the 

 true electro - car- 

 diographic curves* 

 (Fig. 300), which 

 express the actual 

 changes in the po- 

 tential difference 

 between the two 

 points led off. 

 They distinguished 

 in every one of 

 these constructed 

 electro-cardio- 

 grams five points 

 or cusps, three of 



which indicate re- 

 lative negativity 



Fig. 300. Constructed Elec- 

 tro-Cardiograms from Man 

 (Einthoven andLint). Time 

 is laid off along the hori- 

 zontal, and electromotive 

 force along the vertical axis, 

 the same space being allot- 

 ted to ten millivolts (i.e., 

 T ^ volt) as to one second. 



Fig. 301. illustrating the 

 Position of Favourable and 

 Unfavourable Leads for 

 the Human Electro- 

 Cardiogram (Waller). 



* In all accurate work with the capillary electrometer such curves must be 

 obtained by construction from the direct photographic records, which do not 

 themselves give an absolutely true picture of the variations. 



