THE CIRCULATION OF THE BLOOD AND LYMPH 137 



relatively long latent period, marked augmentation. And if 

 the contractions of the heart are registered, the tracing bears 

 a close resemblance to the curve of secondary augmentation 

 following excitation of the mixed nerve on the other side 

 with an equally strong stimulus and for an equal time. 



(3) When the vago-sympathetic is stimulated weakly there 

 is little or no secondary augmentation. Now, it is known 

 that the augmentor fibres require 

 a comparatively strong stimulus 

 to cause any effect when they are 

 separately excited, whereas a weak 

 stimulus will excite the inhibitory 

 fibres. 



The question arises at this point, 

 why it is that, when the inhibitory 

 and augmentor fibres are stimu- 

 lated together in the mixed nerve 

 (and the same is true when the 

 sympathetic on one side and the 

 vagus on the other are stimulated 

 at the same time), the inhibitory 

 effect always comes first, when 



FIG. 48. 



A is a curve representing in 

 an experiment the rate of the 

 t-i-j. rr 1-1 heart before stimulation of the 



there is any inhibitory effect, while sympa thetic, and B the maximum 



the augmentation always has tO rate after stimulation, the number 



follow. The answer has some- 

 times been given, that the latent 

 period of the augmentor fibres is 



of beats per 100" being laid off 

 along the vertical, the temperature 

 of the hearth along the horizontal 

 axis. C is a curve showing the ratio 

 of the frequency after, to that 

 before stimulation of the svm- 



longer than that of the inhibitory Poetic. D shows the absolute 



fibres. But although this is cer- 



amount of acceleration at the 

 various temperatures, the ordi- 

 nates being the excess of the rate 



tainly the Case, the answer is in- after, over that before stimulation. 



sufficient For the period of post- 

 ponement may be much greater than the latent period of 

 the sympathetic fibres when stimulated by themselves. The 

 inhibition apparently runs its course without being affected 

 by the simultaneous augmentor effect, which, lying latent 

 until the end of the inhibition, then bursts out and com- 

 pletes its own curve. It is not like the passing of two waves 

 through each other, but rather like the stopping of one wave 

 until the other has passed by. It seems as if augmenta- 



