60 Dr. A. D. Waller. Various Inclinations of the 



so for the transverse values, which can be directly read off from a sine 

 table ; for the other leads the curves can be verified by working out their 

 appropriate formulse. Tig. 6 is useful as showing at a glance the theoretical 

 values to which the observed values must approximate in the several leads 

 with hearts of various inclinations, and as regards the present paper affords 

 the readiest mode of explanation of the otherwise somewhat perplexing 

 effects of respiration upon the amplitude of the electro-cardiogram. Inspira- 

 tion by reason of descent of the diaphragm and elevation of the ribs causes 

 a clockwise rotation of the electrical axis of the heart, i.e. a diminution of 

 the angle « above and below the heart. Reading the appropriate line on 

 fig. 6 from right to left, i.e. in the direction of inspiratory decrease of «, we 

 see by its rise or fall whether and how much increase or decrease of the 

 ventricular spike is to be anticipated. Thus the transverse must be 

 decreased with inspiration (or increased with expiration) ; the longitudinal, 

 the right superior, and the left inferior increased. And as regards the 

 troublesome case of the two strong leads we realise at a glance how it 

 happens that at high values of x, i.e. with a " horizontal " axis, we find 

 inspiratory increase of the strong leads ; whereas at low values of «, i.e. with 

 an axis at less than 30°, we find inspiratory decrease. 



This figure also supplies an explanation of the following two experiments, 

 one or other of which can nearly always be repeated with success upon 

 a heart of which the electrical axis happens to be of suitable inclination : — 



Experiment 1. — With an approximately horizontal heart the normally 

 negative left inferior spike may be abolished and rendered positive during 

 maximal inspiration. An example of this experiment is given in fig. 7. 



Experiment 2. — With an oblique heart (« = 30° to 45°) the normally 

 positive left inferior spike may be abolished and rendered negative during 

 maximal expiration. An example of this experiment is given in fig. 8. 



[Note. — It is not always easy to decide what are the actual measurements 

 to be taken for calculation. In simple cases, i.e., in cases of vertical heart 

 where Vi is large and positive on both sides, there is no difficulty in 

 determining these values. Nor is there any serious ambiguity for the case 

 of the clearly horizontal heart where Yi is large and at once negative. But 

 the not infrequent cases where Vi is double, composed of a small positive 

 followed by a large negative, or of two small positives separated by a negative 

 movement, cannot be dealt with with the same degree of certainty. The 

 indicator does not take up a decided position, the current axis resultant from 

 opposed and nearly balanced forces fluctuates to and fro, and the obvious 



