PHYSIOLOGY OF ORGANIC LIFE. 121 



we behold in the various secreted fluids that are 

 produced from the blood of the same animal 

 and the medulla of the same plant. Blood 

 bears the same relation to the power which the 

 organs severally possess, as brick and mortar 

 do, to the architect or to the artist, by whom a 

 building is erected. It has no more the power 

 to convert itself into organisation or form, than 

 brick and mortar have, of themselves, the pow- 

 er to erect a building. If it possessed any pow- 

 er of action within itself, by virtue of the sen* 

 sible properties it contains, it would resist the 

 action of the organs to which it was applied, 

 it would act upon them, instead of being chang- 

 ed and converted by them : if it had the power 

 of converting itself, by itself, either into differ- 

 ent organs or into different fluids, the previous 

 existence of those organs would be unnecessary, 

 since the process of conversion and of secretioji 

 would take place without their influence. We 

 might as well suppose, that a building can be 

 erected without hands, and designed without a 

 designer; an effect produced without a produc- 

 ing cause; or, what is equally absurd and 

 false, that the effect and the cause are inherent 

 in one and the same subject. 



By virtue of its passivity, the capacity of 

 blood arises not only of being moved, but of 

 being changed and organised ; it has the capa- 

 city of being moved without having any power 



