66 THE HEART 



slightly before the left, since the wave presumably has less ground 

 to cover to fire off the right auricle. It is usually stated, how- 

 ever, that the auricles beat simultaneously (cf . Tigerstedt and other 

 authorities). According to Arloing and Doyon, however, Chauveau 

 appears to have stated that in the horse the right auricle beats 

 before the left. Frederic q also noticed this in his records on more 

 than one occasion, especially when the heart was beating feebly and 

 slowly. Recently further proof has been forthcoming under his 

 direction. Schmidt-Neelsen finds that normally the right auricle 

 precedes the left. If, however, an extra systole be induced by 

 stimulation of the left auricle, then that auricle precedes the right. 

 Another interesting observation made by him is that when the 

 auricles are induced to beat by stimulation of the ventricle, the 

 right more often precedes the left, but the results are variable. 

 When the heart beats during excitation of the vagus, the normal 

 order of beat is preserved. Stassen finds that in the dog the right 

 auricle precedes the left by '02 to '03 second. He also finds that 

 the ventricles do not beat simultaneously, but that the left nor- 

 mally beats in the dog '03 to '04 second before the right. But 

 when it is stimulated electrically the right precedes the left by 

 a greater time than the left normally precedes the right. From 

 this Stassen infers that there is a form of " antidromic " conduction 

 in the A-V bundle, since if the left be similarly excited, the 

 interval before the right is the same as normal. 



When the auricle beats in the lower vertebrate heart, regurgi- 

 tation is prevented by the action of the venous valves. In the 

 mammal these valves have disappeared, and the prevention of re- 

 gurgitation into the great veins is not altogether effectual. It is on 

 this account that the jugular pulse can be recorded over the jugular 

 bulb even in health. There is undoubtedly a guillotine action by 

 the teenia terminalis tending to prevent regurgitation, but this is 

 insufficient especially with high pressures ; and according to the 

 degree of its insufficiency, so will the jugular tracing vary. Re- 

 gurgitation through the inferior vena cava cannot be prevented 

 by muscle, since there is none. The most important factor here 

 is undoubtedly the high abdominal pressure, and indirectly there- 

 fore the tone of the belly wall. The whole system of abdominal 

 and thoracic veins may be looked upon as a large venous cistern, 

 having a capacity in man of about 430 c.c. The abdominal 

 portion has by far the greater capacity (Keith). The blood is 



