Bauhaus-Universität Weimar

Handbook for the Physiological Laboratory. Text
Burdon-Sanderson, John Scott E. Klein Michael Foster T. Lauder Brunton
(c) In animals of which the vagi are intact, a lung affection is pro¬ 
duced by injecting mucus from the pharynx into the air passages 
which is of the same nature with that now under consideration. 
The combination of these facts leads to the inference that the 
inflammation of the lungs of which animals with divided vagi 
die, is dependent on the intrusion of foreign bodies from the 
pharynx into the air passages and lungs, rather than to any 
direct effect of the section on the lung-tissue. 
102- Demonstration of the Respiratory Functions of 
Afferent Fibres of the Vagus, by Excitation of the Central 
End of the Divided Nerve.—The method of preparing the 
nerve has been already described. The excitor, shown in fig. 225, 
is used. It is better to employ Helmholtz's side wire (see next 
paragraph), but not necessary; for even when strong unmodified 
induced currents are used, there is little danger of unipolar effects, 
the extent to which the nerve can be separated being such, that 
there is no difficulty in interposing a considerable air space be¬ 
tween it and the surrounding parts. 
The phenomena which accompany excitation of the central end 
of the divided vagus vary according to the state of the animal 
and the state of the nerve. It will be convenient to describe 
them under heads corresponding to these conditions :—1 Animal 
breathing naturally. To observe what may be regarded as the 
normal results of excitation, care must be taken that the subject 
of experiment is not exhausted, and that, in placing it on the 
support, nothing is done which can interfere with its breathing. 
The movements of the diaphragm must be recorded * either with 
the aid of the apparatus, fig. 250, or in the manner described 
in the preceding paragraph ; but for the present purpose, by 
far the best method is to introduce into the peritonæal 
cavity, by means of a small opening in the linea alba 
close to the ensiform cartilage, a small flat bag of india-rubber, 
of such size that it can be conveniently slipped between the 
diaphragm and liver. If this bag is slightly distended with air 
and connected with a Marey’s tympanum, it gives excellent 
tracings of the diaphragmatic movements. To the student who 
witnesses the experiment for the first time, a still more con¬ 
vincing mode of appreciating the effect of exciting the central 
end on the diaphragm is to feel the contraction of the muscle 
with the finger during the period of excitation. The nerve 
having been prepared, and the excitor placed under it, a pre¬ 
liminary tracing must be taken of the normal respiration. In 
a tracing, taken by the method described in § 99, it is seen that 
in each respiratory act three parts may be distinguished, one of 
which, the ascent, expresses inspiration, or active contraction 
# See fig. 254 a.


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