74 LAY SERMONS, ADDRESSES, AND REVIEWS. [v. 



Permit me, however, to give more force and clearness 

 to these somewhat abstract considerations, by an illustra- 

 tion or two. 



Imagine a vessel full of water, at the ordinary tem- 

 perature, in an atmosphere saturated with vapour. The 

 quantity and the figure of that water will not change, 

 so far as we know, for ever. 



Suppose a lump of gold be thrown into the vessel — 

 motion and disturbance of figure exactly proportional 

 to the momentum of the gold will take place. But after 

 a time the effects of this disturbance will subside — 

 equilibrium will be restored, and the water will return 

 to its passive state. 



Expose the water to cold — it will solidify — and in so 

 doing its particles will arrange themselves in definite 

 crystalline shapes. But once formed, these crystals 

 change no further. 



• Again, substitute for the lump of gold some substance 

 capable of entering into chemical relations with the 

 water : — say, a mass of that substance which is called 

 " protein ;; — the substance of flesh : — a very considerable 

 disturbance of equilibrium will take place — all sorts of 

 chemical compositions and decompositions will occur ; 

 but in the end, as before, the result will be the resump- 

 tion of a condition of rest. 



Instead of such a mass of dead protein, however, 

 take a particle of living protein — one of those minute 

 microscopic living things which throng our pools, and 

 are known as Infusoria — such a creature, for instance, as 

 an Euglena, and place it in our vessel of water. It is a 

 round mass provided with a long filament^ and except 

 in this peculiarity of shape, presents no appreciable 

 physical or chemical difference whereby it might be 

 distinguished from the particle of dead protein. 



But the difference in the phoenomena to which it 





