292 



THE CIRCULATION OF THE BLOOD 



A tracing showing a higher degree of heart-block is given in Fig. 100. 



Sinus Arrhythmia. In this disorder, which occurs in children and 

 young adults, the heart as a whole is affected, so that the "a," "c" and 

 "v" waves of the jugular tracing are in normal time relations with one 

 another. The pulse is markedly irregular, the irregularity very fre- 

 quently bearing a direct relation to the respirations. A disturbance of 



1 T 



r!t 



Fig. 100. Dropped beats. Second stage of heart-block. (From E. P. Carter.) 



the vagal influence is believed to be concerned with the production of 

 this type of arrhythmia. 



Sinus Bradycardia. The beat originates at long intervals in the 

 sinus; the "a-c" interval is normal, and the radial pulse very slow but 

 practically regular. 



Extrasystoles. These may be either ventricular or auricular in 



Fig. 101. Premature beats (extrasystoles) ventricular in origin at PB. Compare the duration of 

 the intervals marked A and B' with those marked C and D. (From E. P. Carter.) 



origin. In the former case the "a" waves on the jugular tracing space 

 regularly throughout, but the "c" waves at the point of disturbance 

 coincide with the "a" waves, giving therefore a more pronounced wave. 

 This is due to a premature contraction of the ventricle occurring about 



