190 THE NATURE AND ORIGIN OF LIFE 



A muscular element will in vain be irrigated by blood 

 charged with food substances ; it will not assimilate unless 

 it is contracted under the influence of a nerve ; and, not 

 assimilating, it will be slowly destroyed. 



In fact, when the nerve which ends in the muscles of a 

 limb is cut, we see these muscles quickly atrophied although 

 blood continues to reach them. We can sometimes obviate 

 this partially by artificial contractions electrostatic, for 

 example which bring the muscular elements into a state of 

 artificial contraction. 



Accordingly, the histological elements which are governed 

 by nerves are, from the side of assimilation, incomplete 

 elements. This explains the disappearance of useless parts 

 in organisms and the development of those much used. 

 From this point of view the history of the heart is interest- 

 ing. In a normal adult the heart keeps a constant volume. 

 During the periods of repose (diastole) it makes losses which 

 exactly counterbalance its gains in the period of work 

 (systole) . But let any trouble in the general circulation 

 prolong the systole with relation to the diastole and assimila- 

 tion will become greater than destruction and we shall have 

 a case of hypertrophy of the heart. 



