244 ' Einthoven 



about 1"5 cm. The demarcation current of the nerve is compensated in 

 the usual way, and the electrodes are connected with the galvanometer in 

 such a manner that a decrease of the demarcation current, or an action 

 current, causes the image of the string to move in an upward direction. 

 In the accompanying figure, 1 mm. of the abscissa corresponds to 2 sec. ; 

 1 mm. of the ordinates, to 2'7 microvolts. The upper curve (v) represents 

 the action cui-rents of the vagus nerve, and may be called the " electro- 

 vagogram " ; the middle one (p) reproduces the respiratory movements of 

 the animal in such a way that every inspiration corresponds to an ascent 

 and every expiration to a descent of the curve. This pneumogram is 

 obtained by causing the dog to breathe into a large bottle and transmitting 

 the oscillations of the pressure of the air in the bottle to a suitably placed 

 recording Marey's tambour. The lower curve (c) indicates the sphygmogram 

 of the crural artery. 



It can be seen that the electrovagogram exhibits undulations having a 

 double rhythm, viz. : (1) synchronous with the respiratory movements, (2) 

 synchronous with the heart-beats of the animal. That these undulations 

 are caused by the real action currents of the nerve and not by current 

 escape from other organs, can be proved in different ways. 



In the first place we may rely on the method employed, which does 

 not appear subject to this source of error. We have further repeatedly 

 submitted it to the usual proofs of control. Thus, if the nerve is ligatured 

 peripherally to the electrodes or is killed by means of a drop of ammonia, 

 the rliythmic oscillating image of the string is brought completely to rest. 



In the dog, the respiratory oscillations of the right vagus are larger 

 than those of the left one ; while, on the other hand, the heart-beat oscilla- 

 tions of the left vagus surpass those of the same nerve on the right side. 

 In the rabbit the vagus nerve shows exclusively respiratory oscillations, the 

 depressor nerve solely heart-beat oscillations. 



The excitatory state of the vagus endings in the lungs is determined by 

 the volume of these organs and not by the intrapulmonary pressure. If 

 during the cessation of the natural respiratory movements of the animal 

 tlie lungs are insufflated artificially, the electrovagogram shows an undula- 

 tion in the same direction as if the animal is making a natural inspiration. 

 Nevertheless the insufflation is accompanied by an increase, the natural 

 inspiration by a decrease of the intrapulmonary pressure. 



The experiments which we have performed on the effects of insufflating 

 and deflating the lungs have given evidence of the presence of two kinds 

 of pulmonary vagus fibres : those having expiratory and those having 

 inspiratory efiects. The latter act more weakly, are sooner tired, and are 

 killed more easily by injuries than the former, so that the two kinds of 

 fibres can be separated from each other as to their action. Especially is it 

 easy to isolate the effect of the expiratory fibres. The theory of Hering^ 



^ E. Hering, "Die Selbststeuerung der Athiuung dureh den Nervus Vagus," Wiener 

 Sitzungsberichte, 2 Abt., Bd. Ivii., S. 672, 1868. 



