CAUSE OF RESPIRATORY MOVEMENTS. 
289 
for it is the consequence of impressions conveyed to the spinal 
cord, and especially to its upper end, by several nerves,—some 
originating in the lungs, and others in the general surface. 
The nerves originating in the lungs convey to the spinal cord 
the impression produced by the presence of venous blood in 
their capillaries : of this impression we are not ordinarily 
conscious ; but if we hold our breath for a few moments, we 
become aware of it; and it speedily becomes so distressing as 
to force us to breathe, even though we may try to resist it by 
an effort of the will. The impression conveyed by the nerves 
of the general surface is chiefly that produced by the applica¬ 
tion of cold to the skin. It is this which is the cause of the 
first inspiration in the new-born infant; which is not unfre- 
quently prevented by the seclusion of its face (the part most 
capable of receiving this impression) from the influence of the 
air. Every one knows that, when the face is dipped into 
water, an inspiratory movement is strongly excited; and the 
same happens when a glass of water is dashed over the face. 
This simple remedy will often put a stop to hysterical laughter, 
by producing a long sighing inspiration. A still stronger 
tendency to draw-in the breath is experienced in the first 
dash of water over the body in the shower-bath. The respi¬ 
ratory movements, in the higher Animals, are placed under 
the control of the will, to a certain extent, because on them 
depend the production of sounds, and in Man the actions of 
speech; but that they are quite independent of the will, and 
even of sensation, is shown by the fact that they will continue 
after the brain has been completely removed, provided the 
spinal cord and its nerves are left without injury. In most 
of the Invertebrata they are connected with distinct ganglia, 
which minister to them alone. (See Chap, x.) 
341. The actions of sighing , yawning , sobbing , laughing , 
coughing , and sneezing, are nothing else than simple modifica¬ 
tions of the ordinary movements of respiration, excited either 
by mental emotions, or by some stimulus originating in the 
respiratory organs themselves. Sighing is nothing more than 
a very long-drawn inspiration, in which a larger quantity of 
air than usual is made to enter the lungs. This is continually 
taking place in a moderate degree, as already noticed (§ 334); 
and we notice it particularly, when the attention is released 
after having been fixed upon an object which has excited it 
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