364 THE POPULAR SCIENCE MONTHLY. 



contraction ; hence protoplasm may be said to be " contractile" and 

 this is another of its so-called vital properties. 



Protoplasm also feeds upon nutritive material brought into contact 

 with its surface. This it does by flowing around the substance, what- 

 ever it may be, which serves for its food, thus inclosing it in a tem- 

 porary stomach improvised anew for each occasion, and becoming 

 gradually obliterated as the new material slowly dissolves and is ab- 

 sorbed, mingling and chemically combining with the already existing 

 protoplasm, and thenceforth forming a part of its substance. In other 

 words, certain kinds of dead matter called food are assimilated, con- 

 verted into living protoplasm by those processes of absorption and 

 chemical union which constitute nutrition in all living things. Hence, 

 protoplasm is " assimilative" and this is another of its vital properties. 

 Side by side with this process of taking in new material and convert- 

 ing it into its own substance, there is also another process going on 

 that of rejection of old, broken-down, effete matter which has not only 

 become useless to the living protoplasm, but would be injurious if 

 retained. 



The life of protoplasm is thus seen to consist in a double series of 

 chemical changes, by one of which its substance is constantly renewed 

 and built up ; by the other, it as constantly breaks down, the products 

 of decomposition being gradually rejected from the living, ever-fluct- 

 uating mass, which thus becomes the theatre, the arena, of life. 



What is the outcome of this constant play of chemical and phys- 

 ical forces this incessant interchange of matter between the mass of 

 protoplasm and its environment? In other words, what is the mean- 

 ing of the life thus manifested ? Its significance is this : The produc- 

 tion and manifestation of new and higher kinds of force than any 

 belonging to inanimate, inorganic matter. 



In the life of protoplasm we behold the dawning of voluntary mo- 

 tion of those spontaneous movements especially characteristic of ani- 

 mals (though shown to a slight extent by plants as well), and exhibited 

 in the highest degree by man in the thousand muscular adaptations 

 displayed in his complex mechanism. 



But the doctrine of the correlation of forces formulates the fact 

 that the amount of force in the universe of matter is constant and un- 

 varying ;. that, as matter is indestructible, so the forces which it mani- 

 fests are persistent never increasing, never diminishing. Whence, 

 then, comes this new and higher kind of force called spontaneous mo- 

 tion ? It is a law of physics that, as elemental molecules aggregate 

 to form those which are more complex and massive, the force previ- 

 ously manifested by the simpler molecules becomes potential or latent, 

 as it was formerly expressed ; and that in the breaking down of these 

 more complex molecules, in their return to their former simple state, 

 this hidden force springs into activity again, not necessarily reappear- 

 ing, however, as the same kind of force ; there is not only a storing 



