50 MODERN DEFINITIONS OF LIFE. the light of which were read new interpretations of the principle of life. Paracelsus, Van Helmont and Sylvius, could see in its most complicated phenomena nothing but effects of combinations in chemistry. Descartes introduced the new science of mechanics. "The body had been an alembic; now it was a machine. The principles of gravity, mechanics and hydrostatics served to explain the phenomena of the senses, the movements of organs, the exercise of all the functions, and even the acts of intelligence" (Longet). Again, there was reaction toward a vital as distinct from physical force. Haller, who was second only to Harvey, for having revived anew the long neglected studies by direct observation and experiment in lieu of surmise and speculation, discovered the inherent "irritability” in various tissues, a property innate to the tissue itself, and characteristic of living matter. Modern Definitions of Life. The definition of life in our own day has been mostly a play upon words. Bichat says "life is the sum total of the functions which resist death." Lawrence declares it to be “an assemblage of all the functions or purposes of organised bodies, and the general result of their exercise." Lewes defines life as "a series of definite and successive changes without destruction of identity." Duges calls it "the special activity of organized bodies," Beclard, "organisation in action," and Spencer, "the coördination of action." Truly, it might be said of all these phrases, they are only idle repetitions of "life is life." Thus, to define physiology as the science of life, is one thing; but to define life, the subject of which it treats, is another. One might almost say that the definition of life is a rock surrounded with shipwrecked attempts. It is no answer whatever to say that life is a creation. ORGANIC AND INORGANIC MATTER. 51 Such an assertion may satisfy the wants of the emotions, but it will in no way appease the demands of the intellect, trained by cultivation in physical science to entirely ignore unnatural explanations for natural events. Equally empty and evasive in the periphrase that life is the result of all its phenomena. Difference between Organic and Inorganic Matter. May we succeed better, perhaps, with the understanding of life by a comparison between matter endowed with it, and that which is not? Automata have been made to simulate every visible manifestation of life. Vaucanson's duck could walk, talk, i. e., utter sounds (Faber's machine could talk), eat, digest food, and even void per anum indigestible residue. Yet this automaton was wholly built up of wheels and springs, retorts and tubes, mechanical and chemical devices, a cunning contrivance to nearly realise the fanciful conception of Frankenstein. In what respect does such a finished piece of mechanism differ from an organism, a really living thing? It has been said that the activity of an organism is innate, while that of a mechanism is accidental. An animal lives, moves, and has its being of itself, while a machine, steamengine or watch must be supplied with fuel or wound up before its activity is shown. But an organism is no more capable of living without food, than a machine of running without fuel. The food is fuel in a literal sense, and it is the combustion of the food in the body of man, as it is the combustion of fuel in the furnace of the engine, that develops the force in either case. Again, it has been said that activity of some kind or other is essential to the organism, but unessential to the mechanism; that is, if the organism ceases to act, it perishes and is lost, L 52 THE PROPERTY OF ASSIMILATION. whereas an engine remains an engine, or a watch remains a watch, even though not set in motion for years. But we know many organisms that have ceased to show any signs of life for years and yet still exist as such. Small wheellike animals, tardigrades, rotifers, etc., may be completely dried up and kept as lifeless particles for years, to be restored with every manifestation of life, swimming as actively as before, on being put again in water. Frogs and fishes, low in the scale, have been frozen hard into inanimate bodies and again thawed into life. Seeds from the tombs of mummies have been made to germinate and bear fruit after the desiccation of a thousand years. Nor can the much-vaunted power of reproduction be looked upon as a criterion of living things. The power of reproduction is present only at a certain phase of life in all animals and plants, and yet at every period are they none the less alive. Besides, many living things are sterile throughout life, as the workers among bees, the soldiers of ants, hybrids among horses, etc. Nor, again, may it even be maintained that every living thing is descended from a parent like itself; for many species of animals and plants now upon the earth differ so entirely from ancestral forms as to have been long regarded as entirely different species. A skilled zoologist is required to trace the resemblance between fossil and existent forms. The Property of Assimilation. Nevertheless, observes Brücke, who has so clearly established these refutations of long accepted views, we do possess a difference, which enables us to separate living from lifeless matter. Organisms have the property, with which no mechanism of any kind has ever been endowed, of taking up foreign matter and transforming it into their own sub THE PROPERTY OF ASSIMILATION. 53 stance; and the organism grows at the expense of the substance thus acquired. This is the property of assimilation. "It pertains to every organism, so long as it is an organism, and must pertain to every organism, because upon it is based its whole organic life." But if we contrast the growth of an organism with the growth of inorganic matter we may not make this difference so distinct. For, in the first place, we observe that the elements which go to form an organism are not different from those that constitute inorganic matter. The carbon, hydrogen, oxygen and nitrogen of living matter are precisely the same carbon, hydrogen, etc., in the inorganic world. A simple monad, a shapeless mass of protoplasm, scarcely contains as many elements as a piece of common feldspar. That either should increase in size, it must be placed in a medium containing matter like itself, or that may be changed into matter like itself. In the slow evaporation of the solution of a salt, the formation of crystals develops. Each crystal particle grows by addition to its surface. In the growth of an organism the addition is effected from within. So far as growth is concerned the essential difference between the two is merely one of density. Organisms are of soft consistence, hence are penetrable to nutrient matter. Inorganic matter, from its nature, is hard and dense, impenetrable from without. Growth may only take place on its surface, but it is here, as in the organism, always at the expense of the new material. It is true that in the organism the new material is subjected to chemical change, a new arrangement of its atoms resulting from its absorption and assimilation, but this change is due to the fact that carbon, the principal clementary ingredient of organic bodies, has such multitudinous and varied relations with all the other elements. In other words, the various manifestations of life, in its simplest forms at least, admit of explanation on physical 54 PERIOD OF DEVELOPMENT OF LIFE. grounds alone; and, so far as growth and reproduction are concerned, it is no more necessary to invoke the phantom of a mystic vital force in their comprehension, than in the explanation of the form or formation of a crystal in the inorganic world. Whatever theory we may adopt as to the nature of life, there is no longer any doubt as to the Period of its Development upon our Earth, that is, it is positively known that life did not appear coeval with the dissipation of the chaotic confusion which marks the first epoch in every theory of creation. Ages must have lapsed before the necessary conditions of life could have developed. Two theories prevail at present in the civilized world regarding the first creation of life; the so-called miraculous and non-miraculous theories. These theories are more euphemistically designated the teleological and mechanical theories; teleological (reños, end and Zoyos, discourse) because evincing design, according to human conception of the term; and mechanical in the sense of being explicable by the action of natural laws in continuous operation. The miraculous is the supernatural theory as revealed in the first book of Genesis. Because it has received its finest exposition in our day at the hands of the great English poet, Milton, this theory is often called the Miltonic theory. It is depicted in the Bible with the solemn cadence, the metaphor and poetic imagery, the "inspiration," characteristic of the Orient. In its regular sequence of chaos, darkness, absence of form and life, then light, water, vegetation, aquatic life, land life, and, last of all, man, it is in perfect harmony with the natural theory of creation. But, in its disposition of the earth as the center of the universe, and of man as the center of all life, it is directly opposed to all the facts of astronomy, |