On Respiration 209 



muscular substance, not otherwise than in other 

 muscles. 



Wherefore on the suppression of respiration, as 

 that aerial salt required for any motion fails, the 

 beating of the heart and, consequently, the flow of 

 blood to the brain will necessarily be interrupted and 

 death will ensue. But one may live for a certain 

 time without breathing, because the blood contained 

 in the pulmonary vessels and sufficiently impregnated 

 with air is capable of moving the heart at least for a 

 moment. 



And this use of respiration can be further confirmed. 

 For in exercises and violent movements there is need 

 of more intense and more frequent respiration, not so 

 much that a greater flow of blood may pass freely 

 through the lungs — for we have shown that this can 

 take place when respiration stops — but because there 

 is a great expenditure of nitro-aerial salt in conse- 

 quence of the various effervescences made in the 

 contraction of the muscles ; so that the venous blood 

 returns to the heart now much impoverished and 

 thick (and we know that this also happens after 

 convulsive movements in epilepsy). Wherefore, that 

 the effete blood may repair the waste, there is of all 

 things need of more intense respiration. Besides, an 

 acceleration of the heart's beat is necessary in violent 

 movements on account of the more copious flow of 

 blood ; but this can scarcely be effected without freer 

 supply of nitro-aerial particles — especially since the 

 blood is now effete. So that a main use of respiration 

 clearly appears to be to set up the motion of the 

 muscles and especially of the heart. Hence the frog 

 which is accustomed to live under water for some 

 time without respiration will go on living, even when 

 its heart is cut out ; but to animals which require a 



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