ATOMS, MOLECULES, AND CELLS AS FACTORS 139 



The movements of molecules are interesting. 



They are seen in the saUvary cell, in the cells of various plants, such as Chara and Vallisneria, in the migration 

 of pigment in the skin of the frog, &c. Movements may also be witnessed in the molecules of many tissues. Indeed 

 the aggregate of molecular movements and chemical changes in a part, constitute the normal function of such 

 part. The movements occurring in glands and, in the sarcous elements of muscles furnish examples. Molecules 

 move in relays, in succession, and at stated intervals. This arrangement provides for the due nourishment and 

 rest of every part of the plant and animal. Plants and animals take in food, rest, and work betimes. No plant 

 or animal could be continually feeding, continually working, or continually resting. All this is done in due season, 

 and the molecules are primarily concerned. The human heart, as a whole, is at work from the cradle to the grave ; 

 but every part of the heart — all its sarcous or ultimate elements — have their appointed time for working, resting, 

 and feeding. This goes without saying. Any other arrangement is inconceivable. 



Molecules, as a rule, are actuated by two forces ; a force of attraction and a force of repulsion — a centripetal 

 and a centrifugal force. 



Professor J. Tyndall gives a graphic account of the activity of molecules in his address as President of the 

 British Association (1874). He says : " Everywhere throughout our planet we observe a tendency of the ultimate 

 particles of matter to run into symmetric forms. The very molecules appear inspired with a desire for union 

 and growth, and the question of questions at the present day is — and it is one, I fear, which will not be solved 

 in our day, but will continue to agitate and occupy thinking minds after we have departed — this question of questions 

 is. How far does this wondrous display of molecular force extend ? Does it give us the movements of the sap of 

 trees ? I reply with confidence, assuredly it does. Does it give us the beating of our own breasts, the warmth 

 of our own bodies, the circulation of our own blood, and all that thereon depends ? To this question a similar reply 

 must be given." 



As a matter of fact, all movement, of whatever kind, is traceable primarily to atoms and molecules. 

 Less fundamental, but still most important, is the cell. The cell is a distinct entity, and contains, within itself, 

 all the potentialities of independent existence : thus it has a birth, a period of development, a period of maturity, 

 a period of decay and death. Bach cell has a hfe history of its own. There are, as a matter of fact, cell plants and 

 cell animals, where all the functions of life are adequately and faithfully discharged. 



The red-snow plant and oscillatoria consist each of single isolated cells ; the cell performing the function of 

 nutrition and reproduction. The fungi and seaweeds — the so-called cellular plants — are composed of numerous cells, 

 arranged according to a definite order, some of the cells discharging the nutritive and others the reproductive 

 functions. The higher or vascular plants have vessels added to the cells ; the organs of nutrition and reproduction 

 being more compUcated. 



In compound animals, where difierentiation of structure and function are carried to extremes, and where there 

 is the greatest division of labour, the aggregate life of the cells is the hfe of the individual. It follows, that life is, 

 in turn, compoimd, and, as a consequence, there may be particular death, as apart from general death. In other 

 words, parts of plants and animals may and do die ; the plants and animals, as a whole, continuing to live. This 

 is the normal condition of hving plants and animals in a state of health. The living is inextricably mixed up with 

 the dead. The new matter added to both is dead. The effete or waste products are also dead. The hving 

 substance occupies an intermediate position. It exercises the power of selecting, seizing, appropriating, and 

 assimilating new matter, while it discharges the used up or effete products. That hving plants and animals 

 may be infinitely minute is abundantly proved by the presence everywhere, in incalculable numbers, of micro- 

 organisms the very existence of which was not even suspected until quite recently. These remarks apply not 

 only to plants and animals as wholes, but to hving cells, and to every plant and animal structure, whether hard 

 or soft. 



The subtle element of life moves mysteriously amongst matter, and is unquestionably superior to it. 

 Life in plants and animals is, as it were, surrounded by a material atmosphere of death. 



The cell is regarded by most authors as the starting-point for all structure and function in plants and animals. 

 This view was strongly urged by Professor Rudolf Virchow. 



As already explained, I regard growth and organisation as, primarily, the product of life acting on the atoms 

 and molecules which constitute the cell. So far as I can make out, it is in atomic and molecular protoplasm that 

 all the fundamental changes which result in development and differentiation occur. 



This seems satisfactorily proved by the fact that spores, germs, seeds, and eggs, which are apparently honio- 

 geneous and identical in aU their parts and particles, do, nevertheless, vary infinitely, each producing only its 

 own kind. 



The difficulty experienced by investigators in referring the beginning of growth, development, reproduction, 



