Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
2 74 
the spinal cord is divided immediately below the medulla oblongata, 
the effect is modified not only by the destruction of the accelerator 
nerves, but by the general paralysis of the vasomotor system. 
Consequently no answer to the question is to be obtained by direct 
observation of the changes which are produced by any such opera¬ 
tion in the rate of pulsation of the heart, so that the end we have 
in view can only be accomplished indirectly. We already know 
that both vagi are in constant action, i.e.} that the heart is 
constantly under their inhibitory control; and that when this 
control is removed by dividing them, the frequency of the pulse 
increases. It is obvious that this effect can only be witnessed so 
long as the control is in actual exercise ; in other words, that if the 
vagi are not acting, it would make no difference as regards the 
heart whether they are divided or not. The consideration of this 
fact suggests the method which is employed in the experiment above 
described, which shows that in an animal in which the spinal 
cord has been divided below the medulla, the rate of the pulse is 
the same before and after section of the vagi. 
Bernstein has further shown that the same thing happens after 
destruction of the whole ganglionic cord, or of the cervical part, 
provided that the spinal cord is at the same time severed at the 
seventh vertebra. In the dog, section of the cord generally 
diminishes the frequency of the pulse. There is no such effect in 
"die rabbit. The difference can only be explained by supposing 
that in the former the activity of the accelerator nerves is less, as 
compared with that of the nerves in reflex relation with the vagus, 
than in the latter. In the frog, section of the sympathetic at the 
level of the junction of the aortæ has no direct effect on the 
frequency of the pulse, for the same reason, viz., that in this animal 
the heart-beat is not quickened by section of the vagi. 
The influence of reflex excitation of the vagus through the fifth 
nerve may be easily shown in the rabbit by causing the animal to smell 
ammonia. The effect is immediate. According to the strength of the 
ammonia, the heart is arrested in diastole, or the diastolic intervals 
are lengthened. The inhalation of chloroform, which is so apt to 
be fatal to rabbits, stops the heart in the same way. When sudden 
death occurs in man by a blow on the epigastrium, or by drinking 
a large quantity of cold water, the heart is arrested in diastole by 
the agency of the same nerves as in Goltzes experiment. 
79. Demonstration of the Influence of Increase or Dimi¬ 
nution of the Arterial Pressure on the Frequency of the 
Contractions of the Heart.—The pulse is retarded by increase, 
accelerated by diminution of arterial pressure. That these effects 
are mainly dependent on the inhibitory heart nerves, can be shown 
in the rabbit as follows :—Ligatures having been passed round the 
vagus nerve on each side, and a needle inserted in the heart, the


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