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Physiology. — "An investigation on the quantitative relation be- 

 tioeen vagus stimulation and cardiac action, on account of 

 an experimental investigation of Mr. P. Wolterson" '). By 

 Prof. H. Zwaardemaker. 



(Communicated in the meeting of December 29, 1906). 



The experiments were performed on Einys orbicularis, whose right 

 nervus vagus was stimulated by means of condensator charges and 

 non-polarising electrodes of Donders 2 ), while auricle and ventricle 

 were recorded by the suspension method. The mica-condensators had 

 a capacity of 0,02, 0,2 and 1 microfarad, the voltage varied from 

 a fraction of a volt to 12 volts, occasionally even more. From this 

 the intensity of the stimulus was calculated in ergs (or in coulombs 

 by Hoorwkg's method). Only a part of this energy, passing through 

 the nerve, when it is charged, acts as a stimulus. What part this is 

 remains unknown, but it is supposed not to vary too much in the 

 same set of experiments. In the typical experiments a summation 

 took place of ten stimuli, succeeding each other in tempos of 7s 

 second; in particular experiments single stimuli or other summations 

 were investigated. Of fatigue little evidence is i'ound with our mode 

 of experimenting, rather a somewhat increased sensitiveness of the 

 vagus system towards the end of a set of experiments. 



Stimulation of the right vagus produces in the tortoise in the first 

 place lengthening of the duration of a cardiac period 3 ), in such a 

 way that in the second period, after a stimulus, starting during 

 the cardiac pause, the diastolic half of the period is considerably 

 retarded, while in some subsequent periods a decreasing retardation 

 of the diastolic part of the period is noticed. 



Then stimulation of the vagus causes contraction to become feebler, 

 this phenomenon becoming gradually more distinct and reaching its 

 maximum some periods after stimulation. This decrease of contractile 

 power is primary, since it may also occur when any change in the 

 automatic action is absent (e.g. when the stimulus consists of one 

 condensator charge and when the left vagus is stimulated). Finally 

 vagus stimulation as a rule produces slackening of the tonus, rarely 

 tonic heightening. Changes in conductivity were only observed once. 



!) For details we refer to the author's academical thesis, which will be published 

 ere long. 



2 ) Onderzoekingen Phys. Lab. Utrecht (3) Vol I p. 4, PI. I, fig. 1, 1872. 



3 ) The duration of a cardiac period is reckoned from the foot-point of a sinusal 

 contraction or if tliis is not visible, of an auricular contraction, to the foot-point 

 of the next following sinusal resp. auricular contraction. 



