1898] CELL-PHYSIOLOGY 309 



which excites another part ; but in the developed form a differentia- 

 tion of the two has taken place. All higher types exhibit this 

 differentiation. Be it muscle or gland or other operating organ, the 

 cause of its activity lies not in itself but in a nervous agent, local 

 or central, with which it is connected. Hence, then, there is 

 congruity between the above interpretation and certain general 

 truths displayed by animal organisation at large. We may infer 

 that in a way parallel to that just indicated, cell-evolution was, 

 under one of its aspects, a change from a stage in which the exciting 

 substance and the substance excited were mingled with approximate 

 uniformity, to a stage in which the exciting substance was gathered 

 together into the nucleus and finallv into the chromosomes : leaving 

 behind the substance excited, now distinguished as cytoplasm. 



Some further general aspects of the phenomena appear to be in 

 harmony with this interpretation. Let us glance at them. 



There is good reason for concluding that in the animal organism 

 nitrogenous substances play the part of decomposing agents to the 

 carbo-hydrates — that the molecular disturbance set up by the collapse 

 of a proteid molecule destroys the equilibrium of sundry adjacent 

 carbo-hydrate molecules, and causes that evolution of energy which 

 accompanies their fall into molecules of simpler compounds. Here, 

 if the foregoing argument is valid, we may conclude that this highly 

 complex phosphorised compound which chromatin contains plays the 

 same part to the adjacent nitrogenous compounds as these play to 

 the carbo-hydrates. It may be pointed out that in animal organisms 

 the various structures are so arranged that evolution of a small 

 amount of energy in one, sets up evolution of a larger amount of 

 energy in another; and often this multiplied energy undergoes a 

 second multiplication of like kind. If this view is tenable, we may 

 now suspect that this method displayed in the structures of the 

 Metazoa was initiated in the structures of the Protozoa, and conse- 

 quently characterises those homologues of them which compose the 

 Metazoa. 



When contemplated from the suggested point of view, karyo- 

 kinesis appears to be not wholly incomprehensible. For if the 

 chromatin yields the energy which initiates changes throughout the 

 rest of the cell, we may see why there eventually arises a process 

 for exact halving of the chromatin in a mother-cell between two 

 daughter-cells. To make clear the reason, let us suppose the por- 

 tioning out of the chromatin leaves one of the two with a sensibly 

 smaller amount than the other. What must result ? Its source of 

 activity being relatively less, its rate of growth and its energy of 

 action will be less. If a protozoon, the weaker progeny arising by 

 division of it will originate an inferior stirp, unable to compete 



