SUMMARY OF PHYSIOLOGICAL DEVELOPMENT. 393 



the tissue must have their molecular arrangements changed, 

 and the change in their molecular arrangements must go on 

 until their molecular motions are so re-adjusted as to equili 

 brate the molecular motions of the new physico-chemical or 

 chemical agent. In other words, the organic matter com 

 posing the part, if it continues to be organic matter at all, 

 must assume that molecular composition which enables it to 

 bear, or as we say adapts it to, the incident forces. 



Nor is it less certain that throughout the organism as a 

 whole, equilibration is alike the proximate limit of the changes 

 wrought by each action, as well as the ultimate limit of the 

 changes wrought by any recurrent actions or continuous 

 action. The movements every instant going on, are move 

 ments towards a new state of equilibrium. Eaising a limb 

 causes a simultaneous shifting of the centre of gravity, and 

 such altered tensions and pressures throughout the body as 

 re-adjust the disturbed balance. Passage of liquid into or 

 out of a tissue, implies some excess of force in one direction 

 there at work ; and ceases only when the force so diminishes or 

 the counter-forces so increase that the excess disappears. A 

 nervous discharge is reflected and re-reflected from part to 

 part, until it has all been used up in the re-arrangements pro 

 duced equilibrated by the reactions called out. And what 

 is thus obviously true of every normal change, is equally true 

 of every abnormal change every disturbance of the estab 

 lished rhythm of the functions. If such disturbance is a 

 single one, the perturbations set up by it, reverberating 

 throughout the system, leave its moving equilibrium slightly 

 altered. If the disturbance is repeated or persistent, its suc 

 cessive effects accumulate until they have produced a new 

 moving equilibrium adjusted to the new force. 



Each re-balancing of actions, having for its necessary con 

 comitant a modification of tissues, it is an obvious corollary 

 that organisms subjected to successive changes of conditions, 

 must undergo successive differentiations and re-differentia 

 tions. Direct equilibration in organisms, with all its accom- 



