PERSISTENCE OF FORCE. 177 



lent to somewhat the same force used in the development of 

 another animal, there must needs be shown a resemblance. 

 Persistence of force, therefore, shows a necessity for the belief 

 in the gradual evolution of one type from another, in all cases 

 where conditions of life are becoming more complex. 



At the birth of the young being development does not cease. 

 The parts are continually gaining in power, and are changing 

 in form throughout the period of youth. As the infant 

 increases in age he develops more capabilities, either through 

 the perfection of old or the formation of additional structure. 

 As the forces decrease in intensity the child — now become a 

 man — is said to be growing old ; and when the forces give 

 out, then development ceases ; there is no capacity for the 

 gathering in of the power that is necessary to supply the 

 force consumed in the labor of living, and death ensues. 

 Partial failure to meet this equilibrium may produce disease 

 only, and the patient, by gradually regaining this equilibrium 

 between expenditure and supply, may recover his health. 



Life and death, development, reproduction, generation, — 

 all are the expression of the effects under general laws, of 

 which that of persistence of force is the ebii f. Inheritance 

 is shown in development, as in ovulation and generation. It 

 is but the expression of facts of our observation ; and it is 

 by the study of development that we are able to assert that 

 heredity is an expression of the action of general law — per- 

 sistence of force as applied to vitality ; — a law so powerful 

 and universal in its conception, that once giveu vitality and 

 constant change of environment, and if vitality endures, devel- 

 opment must of necessity ensue. In each, cause must produce 

 an effect, and we thus have change. In the change we cannot 

 conceive of no effect following the altered circumstance, so 

 that neither the cells nor their concretion, the body, after 

 once having undergone a change, can transmit the same 

 qualities or forces that they could have done if unchanged. 

 By the same law, transmissal or development of forces can 

 only take place in accordance with the order in which they 

 were received, for force modifies force ; and no concrete 

 force could be just what it is had there been any change 

 in any of the individual forces, whose totality is the result 

 before us. 



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