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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