Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
must be distant from the primary one, is cautiously brought nearer 
to it until this effect is produced. As soon as this is the case, it is 
usually observed that the artery of the ear, instead of contracting, 
dilates, and that the whole lobe obviously contains more blood than 
it did before. Frequently, however, it happens that, notwithstanding 
the increase of arterial pressure, no increased vascular injection is 
observable. In this case, recourse must be had to the posterior auri¬ 
cular nerve, the excitation of the central end of which is almost cer¬ 
tain to be followed by the effect in question. The augmentation of 
arterial pressure and the dilatation of the auricular artery appear 
to be collateral phenomena, both increasing gradually during the 
few seconds which succeed the commencement of electrical excita¬ 
tion. If care is taken neither to prolong the excitation unduly 
nor to use too strong currents, the reaction may be witnessed a 
great number of times in the same animal. 
54. (2.) Excitation of the Dorsalis Pedis.—When the cen¬ 
tral end of the divided dorsal nerve of the foot is excited, pheno¬ 
mena occur of a similar nature. To enable the observer to judge 
of the effect, the saphenous artery must be exposed in its course 
down the inner side of the lower half of the thigh, as recommended 
in § 49, p. 241. It is then seen that during and after excitation of 
the central end of the divided nerve, the artery gradually dilates, 
subsequently regaining its former dimensions. 
The general result of the preceding experiments may be ex¬ 
pressed by saying that the afferent nerves to which they relate (in 
common probably with other sensory nerves) contain fibres so 
endowed that, when they are excited, the action of the vasomotor 
centre is inhibited or suspended, as regards certain regions with 
which the nerves in question are in close anatomical relation. 
In its relations to the vasomotor nervous system, the words “ inhibi¬ 
tory ” and “ depressor,” both of which are used by physiologists 
to denote the case in which arterial tonus is diminished by excita¬ 
tion of an afferent nerve, may be regarded as equivalent. 
Experiments relating to the effects of direct Excitation and 
Division of the Yasomotor Nerves. 
When a vasomotor nerve is excited directly, the arteries of the 
region to which it is distributed contract. When it is divided, they 
become permanently larger, and remain unaffected by changes in 
the condition of the vasomotor centre, whether these are deter¬ 
mined by direct or reflex excitation. 
55. (1.) Demonstration of the Vasomotor Functions of 
the Cervical Portion of the Sympathetic Nervous System 
in the Rabbit.—In 1852, Brown-Séquard showed that when the


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