What makes protoplasm and its modifications still more marvellous is the power it possesses of absorbing and moulding a number of other elements in various parts of living organisms for special uses. Such are silica in the stems of the grass family, lime and magnesia in the bones of animals, iron in blood, and many others. Besides the four elements constituting protoplasm, most animals and plants contain also in some parts of their structure sulphur, phosphorus, chlorine, silicon, sodium, potassium, calcium, magnesium, and iron; while, less frequently, fluorine, iodine, bromine, lithium, copper, manganese, and aluminium are also found in special organs or structures; and the molecules of all these are carried by the protoplasmic fluids to the places where they are required and built into the living structure, with the same precision and for similar ends as brick and stone, iron, slate, wood, and glass are each utilised in their proper places in any large building.[14] The organism, however, is not built, but grows. Every organ, every fibre, cell, or tissue is formed from diverse materials, which are first decomposed into their elementary molecules, transformed by the protoplasm or by special solvents formed from it, carried to the places where they are needed by the vital fluids, and there built up atom by atom or molecule by molecule into the special structures of which they are to form a part.
But even this marvel of growth and repair of every individual organism is far surpassed by the greater marvel of reproduction. Every living thing of the higher orders arises from a single microscopic cell, when fertilised, as it is termed, by the absorption of another microscopic cell derived from a different individual. These cells are often, even under the highest powers of the microscope, hardly distinguishable from other cells which occur in all animals and plants and of which their structure is built up; yet these special cells begin to grow in a totally different manner, and instead of forming one particular part of the organism, develop inevitably into a complete living thing with all the organs, powers, and peculiarities of its parents, so as to be recognisably of the same species. If the simple growth of the fully formed organism is a mystery, what of this growth of thousands of complex organisms each with all its special peculiarities, yet all arising from minute germs or cells the diverse natures of which are wholly indistinguishable by the highest powers of the microscope? This, too, is said to be the work of protoplasm under the influence of heat and moisture, and modern physiologists hope some day to learn 'how it is done.' It may be well here to give the views of a modern writer on this point. Referring to a difficulty which had been stated by Clerk-Maxwell twenty-five years ago, that there was not room in the reproductive cell for the millions of molecules needed to serve as the units of growth for all the different structures in the body of the higher animals, Professor M'Kendrick says:—'But to-day, it is reasonable from existing data to suppose that the germinal vesicle might contain a million of millions of organic molecules. Complex arrangements of these molecules suited for the development of all the parts of a highly complicated organism, might satisfy all the demands of the theory of heredity. Doubtless the germ was a material system through and through. The conception of the physicist was, that molecules were in various states of movement; and the thinkers were striving toward a kinetic theory of molecules and of atoms of solid matter, which might be as fruitful as the kinetic theory of gases. There were motions atomic and molecular. It was conceivable that the peculiarities of vital action might be determined by the kind of motion that took place in the molecules of what we call living matter. It might be different in kind from some of the motions dealt with by physicists. Life is continually being created from non-living material—such, at least, is the existing view of growth by the assimilation of food. The creation of living matter out of non-living may be the transmission to the dead matter of molecular motions which are sui generis in form.' This is the modern physiological view of 'how it may be done,' and it seems hardly more intelligible than the very old theory of the origin of stone axes, given by Adrianus Tollius in 1649, and quoted by Mr. E.B. Tylor, who says:—'He gives drawings of some ordinary stone axes and hammers and tells how naturalists say that they are generated in the sky by a fulgureous exhalation conglobed in a cloud by the circumfixed humour, and are, as it were, baked hard by intense heat, and the weapon becomes pointed by the damp mixed with it flying from the dry part, and leaving the other end denser, but the exhalations press it so hard that it breaks through the cloud and makes thunder and lightning. But—he says—if this is really the way in which they are generated, it is odd they are not round, and that they have holes through them. It is hardly to be believed, he thinks.'[15] And so, when the physiologists, determined to avoid the assumption of anything beyond matter and motion in the germ, impute the whole development and growth of the elephant or of man from minute cells internally alike, by means of 'kinds of motion' and the 'transmission of motions which are sui generis in form,' many of us will be inclined to say with the old author—'It is hardly to be believed, I think.'
This brief statement of the conclusions arrived at by chemists and physiologists as to the composition and structure of organised living things has been thought advisable, because the non-scientific reader has often no conception of the incomparable marvel and mystery of the life-processes he has always seen going on, silently and almost unnoticed, in the world around him. And this is still more the case now that two-thirds of our population are crowded into cities where, removed from all the occupations, the charms, and the interests of country life, they are driven to seek occupation and excitement in the theatre, the music-hall, or the tavern. How little do these know what they lose by being thus shut out from all quiet intercourse with nature; its soothing sights and sounds; its exquisite beauties of form and colour; its endless mysteries of birth, and life, and death. Most people give scientific men credit for much greater knowledge than they possess in these matters; and many educated readers will, I feel sure, be surprised to find that even such apparently simple phenomena as the rise of the sap in trees are not yet completely explained. As to the deeper problems of life, and growth, and reproduction, though our physiologists have learned an infinite amount of curious or instructive facts, they can give us no intelligible explanation of them.
The endless complexities and confusing amount of detail in all treatises on the physiology of animals and plants are such, that the average reader is overwhelmed with the mass of knowledge presented to him, and concludes that after such elaborate researches everything must be known, and that the almost universal protests against the need of any causes but the mechanical, physical, and chemical laws and forces are well founded. I have, therefore, thought it advisable to present a kind of bird's-eye view of the subject, and to show, in the words of the greatest living authorities on these matters, both how complex are the phenomena and how far our teachers are from being able to give us any adequate explanation of them.
I venture to hope that the very brief sketch of the subject I have been able to give will enable my readers to form some faint general conception of the infinite complexity of life and the various problems connected with it; and that they will thus be the better enabled to appreciate the extreme delicacy of those adjustments, those forces, and those complex conditions of the environment, that alone render life, and above all the grand age-long panorama of the development of life, in any way possible. It is to these conditions, as they prevail in the world around us, that we will now direct our attention.