THE FOECES IN THE ORGANISM 53 



effect. If, on the other hand, the normal stimulus is absent 

 there follows of necessity a weakening and decrease. The 

 much-exercised muscle grows in volume and correspondingly 

 in working power, the unused muscle becomes powerless and 

 atrophied. 



Most clearly is the degeneration of muscular tissue observed 

 in pathological changes, as, for instance, in a badly healed joint. 

 Here the blood supply is exactly the same as in the healthy 

 organs, but the functional stimulus is absent, and thus degenera- 

 tion sets in. A similar result is observed when we sever the 

 nerve conveying the stimulus : decrease in volume and symptoms 

 of degeneration become quickly noticeable in the muscle, and 

 complete destruction of the structure is not infrequently the 

 final result. Or, to give another instance, when in a human being 

 one kidney degenerates and loses its functions, or is removed by 

 an operation, the other kidney, owing to the greater demands 

 made upon it, increases enormously in volume, often to more 

 than double its usual size. 



But as the organism has at its disposal, at any rate 

 within certain limits, a circumscribed amount of building 

 material in which all its various parts share, it follows that 

 the excess of food used by a certain organ or tissue, owing to 

 increased activity, must be taken away from another less used 

 organ. In proportion, therefore, to their importance or " out- 

 put of work " the various parts of the animal body maintain 

 an unstable equilibrium, and, on the whole, prevent that one part 

 exceeds its normal ''allowance" at the expense of the rest, at 

 any rate as long as the welfare of the whole body does not 

 justify the excess. There is going on, metaphorically speaking, 

 a restless competition a struggle of the parts for the available 

 sources of food in the living body. Though perhaps this point 

 would be more appropriately mentioned in another place, it 

 seems nevertheless advisable, on account of its great importance, 

 to anticipate some of the points and deal with them here. 



An organ in which this struggle of the parts may be most 

 clearly observed for it is here the entire cells which enter into 

 direct competition is the male and female generative gland of 

 many animals. A little cuttle-fish from the Gulf of Naples may 

 serve as an illustration. If we observe thin transverse sections 



