24 



ANIMAL MECHANICS. 



tuning fork properly weighted, and considered the number of 

 vibrations to amount to only 6 per second, which is lower 

 than two octaves below the normal CCC. 



A friend of mine, aged forty-five years, who was a seven 

 months' child, prematurely born while his mother was dan- 

 gerously ill of typhus fever, has had slight congenital paralysis 

 agitans of the right arm, forearm, and hand, all through his 

 life ; this gentleman was carefully examined by me in August, 

 1863, with the result that his muscular susurrus in the arm 

 affected had only the pitch of 4 beats per second, although 

 the susurrus of the other arm is of the usual note. 



I have also ascertained, by over-fatiguing the forearm by 

 racket playing, that the pitch of the muscular susurrus is 

 lowered, and that a sensible paralysis agitans of a temporary 

 character is set up by the over-exertion. 



I have not been able to verify the continuance of the 

 susurrus after death, except in cases of tetanus, nor have I 

 succeeded in observing it in amputated limbs ; but I have no 

 doubt, from the published results of Dr. Collongues' careful 

 observations, that my failure is simply the result of a deficiency 

 in my own powers of observation, and that the susurrus may 

 continue audible to more delicately organized ears than my 

 own, long after death or amputation. 



3. On the Statical Work done by Muscles in continued 

 Contraction. — Muscles may be employed either in continuous 

 statical work resisting pressure, or in dynamical work, lifting 

 weights with intervals of repose. The work done by muscles 

 in the latter case is easily measured by measuring the ex- 

 ternal resistances overcome ; while in the estimation of stati- 

 cal work, there is much difficulty in obtaining numerical 

 estimates of the work actually done : at the same time there 

 is no doubt as to the reality of the work, for the muscles 

 become rapidly fatigued when employed in doing statical 

 work. 



