130 



APPLIED PHYSIOLOGY 



What the advantage to the organism of many of the 

 disturbances of the heart brought about by nervous 

 influences may be it is often hard to say, but probably 

 we shall not be far wrong if we regard most of them as 

 essentially protective and compensatory in their nature. 

 In particular, they seem to be designed to mitigate 

 the effects of sudden rises of blood-pressure, especially, 

 perhaps, on the heart itself ; for all rises of arterial 

 pressure seem to induce a slowing and enfeeblement of 

 the heart's action, whilst, conversely, sudden falls of 

 pressure are attended by a more frequent and powerful 

 heart-beat. In this way, too, the heart itself is protected 

 from undue strain. 



3. The ability to exercise any voluntary control over 

 the nervous mechanism of the heart is a phenomenon of 

 the rarest occurrence. The best example of it is the 

 classical case of Colonel Townshend, recorded by Dr. 

 George Cheyne,* who, when on his death-bed, was able 

 to throw himself at will into a state of suspended anima- 

 tion, in which the heart's action became imperceptible. 

 There are other cases on record as well, in which the 

 heart's rate could be voluntarily increased, and in all 

 such instances there has been an unusual degree of 

 control over the involuntary muscles, t 



The Rhythm of the Heart. 



The maintenance of the regularity or otherwise of th< 

 rhythm of the heart depends upon two factors : (1) th< 



* 'The Case of the Hon. Colonel Townshend,' 'The Englu 

 Malady,' fourth edition, 1734. 

 f See Eeid Hunt, Amer. Journ. of Physiol., 1899, ii. 395. 



