MUSKENS. — ACTION OP THE VAGUS NERVE. 187 



of different parts of the heart. It is easy to prove that the diminished 

 force of the ventricular contractions in Vagus stimulation as studied 

 by Heideuhain and Gaskell can be observed only in cases of imperfect 

 nutrition caused, for instance, by loss of blood. There is no reason to 

 believe that the Vagus nerve has any influence upon the force of the nor- 

 mally nourished ventricle or upon that of the normally nourished veins, 

 although a negative influence of Vagus stimulation upon the force of the 

 auricle seems to be a constant effect. The phenomena described by 

 Heidenhain and Gaskell may perhaps belong in the same category as the 

 " staircase " of Bowditch ; at all events, I could in the American bull-frog 

 (R. Catesbeiana) easily demonstrate, as an effect of stimulation after 

 bleeding, a rapid decrease or disappearance of the ventricular contractions, 

 which simulates a standstill. After this standstill the contractions came 

 gradually back to their former force. The same staircase-like phenome- 

 non can, after somewhat more prolonged anaemia, be observed also in the 

 auricle, not, however, in the large veins. 



A third point in my experiments which may be worthy of mention is 

 the manner in which I stimulated the Vagus. I needed to find a method 

 which can be used without any operation or loss of blood. Moreover, 

 it was desirable to stimulate both Vagi, as one often finds them not 

 equally effective. For this purpose a special instrument was constructed, 

 which is to be fixed in the Tubae Eustachii, and which will hereafter be 

 fully described. Of the details I will mention here merely that twenty- 

 four hours before the experiment the animal received a small dose of 

 curare, which was insufficient to cause complete paralysis. It may also 

 be mentioned, that I have made a special study of the analysis of physio- 

 logical standstills, which last from some seconds to half a minute. In 

 frogs, with good reflex irritability, treated as above described, one very 

 often sees, without any stimulation, spontaneous standstills. These nor- 

 mal standstills never last so long as, for instance, those observed by 

 Gaskell with prolonged faradization. I have avoided these standstills, in 

 the conviction that in that way new factors are introduced, viz. insufficient 

 nutrition during and after a standstill. 



The analysis of the dromotropic * and of the chronotropic f effect of the 

 Vagus upon the different parts of the heart is attended with the greatest 

 difficulties. The further the analysis proceeds the more it becomes ob- 

 vious that phenomena apparently belonging to the chronotropic effect can 



* Influencing the conducting power. 



t Influencing the frequency of the contractions. 



