Chap. IX. DECISION. 235 



tion, and then to cease breathing; but he thinks that 

 Sir C. Bell's explanation is erroneous. lie maintains 

 that arrested respiration retards the circulation of the 

 blood, of which I believe there is no doubt, and he ad- 

 duces some curious evidence from the structure of the 

 lower animals, showing, on the one hand, that a retarded 

 circulation is necessary for prolonged muscular exertion, 

 and, on the other hand, that a rapid circulation is neces- 

 sary for rapid movements. According to this view, when 

 we commence any great exertion, we close our mouths 

 and stop breathing, in order to retard the circulation of 

 the blood. Gratiolet sums up the subject by saying, 

 " C'est la la vraie theorie de l'effort continu; " but how 

 far this theory is admitted by other physiologists I do 

 not know. 



Dr. Piderit accounts 15 for the firm closure of the 

 mouth during strong muscular exertion, on the principle 

 that the influence of the will spreads to other muscles be- 

 sides those necessarily brought into action in making any 

 particular exertion; and it is natural that the muscles 

 of respiration and of the mouth, from being so habit- 

 ually used, should be especially liable to be thus acted 

 on. It appears to me that there probably is some truth 

 in this view, for we are apt to press the teeth hard to- 

 gether during violent exertion, and this is not requisite 

 to prevent expiration, whilst the muscles of the chest 

 are strongly contracted. 



Lastly, when a man has to perform some delicate and 

 difficult operation, not requiring the exertion of any 

 strength, he nevertheless generally closes his mouth and 

 ceases for a time to breathe; but he acts thus in order 

 that the movements of his chest may not disturb those 

 of his arms. A person, for instance, whilst threading a 



18 ' Mimik unci Phvsiog-nomik,' s. 79. 



