Spencee. — On Life. 117 



Animals and plants derive their nourislimeut from different sources. The 

 pabulum of the vegetable kingdom is derived from the inorganic world in 

 the form of water, carbonic acid, and ammonia. Animals, on the other 

 hand, are unable to assimilate these simple compounds, and can only live 

 on protoplasm already prepared for them, either by vegetables or by other 

 animals, which have, in their turn, absorbed previous vegetable protoplasm 

 into their own bodies. Again animal and vegetable chemistry are, as it 

 were, essentially antagonistic. The chemistry of vegetable life is synthetic, 

 it takes simple compoimds and, after rejecting those portions it does not 

 require, builds of the remainder compound substances of great complexity. 

 Animal chemical processes are analytic ; they consist in seizing these highly 

 complex matters, and reducing them to the simple compounds in which 

 they originally existed. 



From this we learn that the essential element of Ufe consists in the 

 eternal and incessant circulation of matter. The vegetable kingdom takes 

 water, carbonic acid, and ammonia, separates and discharges the oxygen it 

 does not require, for the use of the animal kingdom, forms complex com- 

 pounds of the remainder — protoplasm, vegetable albumen, gluten, starches, 

 oils, fats, sugars for food, those volatile oils to which the scent of flowers is 

 due, resins, camphors, guttapercha, turpentines, india-rubber, alkaloids as 

 quinine, morphine, strychnine, and many others ; indeed, the number of 

 these vegetable products is infinite. Again, animals seize upon the oxygen 

 exhaled by plants, and convert it into carbonic acid. They feed upon the 

 protoplasm provided for them by the vegetable kingdom, and after utilizing 

 it for the higher functions of animal life — locomotion, consciousness, sensa- 

 tion, thought, reason — they return it to the inorganic kingdom as water, 

 carbonic acid, and ammonia, to be again taken up by vegetables, and recom- 

 mence the never ending cycle of physical and chemical change. Letourneau 

 remarks, "In living beings, in effect, matter is in a state of extreme 

 mobility ; it is subject to a perpetual movement of combination and decom- 

 bination, without repose, without truce ; its elements go and come, have 

 reciprocities of action, aggregate themselves, disaggregate themselves ; there 

 is a whfrl of atoms amongst unstable compounds, capable of forming, dis- 

 aggregating, metamorphosing themselves, of renewing the woof of the living 

 tissues." And Professor Huxley tells us that, "the wonderful noon-day 

 silence of the tropical forests is, after all, only due to the dullness of our 

 hearing ; and could our ears catch the murmur of the molecules as they 

 whirl in the innumerable myriads of living cells which constitute each tree, 

 we should be deafened as with the roar of a mighty city." 



If you have followed me hitherto you will see that all the physical and 

 chemical phenomena of life which I have endeavoured to describe are purely 



