It may be asked, however, Why is a sense of mystery especially evoked in some minds by the contemplation of life? Partly, I think, because the scientific interpretation of organic processes is so recent, and in many respects so incomplete. People have grown so accustomed to the metaphysical assumptions employed by physicists and chemists when they speak of the architecture of crystalline forces and the selective affinity of atoms, they have been wont for so long to accept the "mysteries" of crystallisation and of chemical union, that the metaphysical causes have coalesced with the descriptions and explanations of science, and the joint products are now, through custom, cheerfully accepted as "natural." Where the phenomena presented by protoplasm are in question, this coalescence has not yet taken place; the metaphysical element is on the one hand proclaimed as inexplicable on naturalistic methods of interpretation, and on the other hand denied even by those who talk glibly of physical forces. But in due course of time this, too, will be commonly accepted as perfectly natural, and the battle will rage elsewhere.
Our attitude towards the vexed question of Vitalism, or the existence of a specific Vital Force, must depend on whether we regard the question from a strictly scientific or from a metaphysical standpoint. It is unnecessary to enter at any length into the past history of the subject. Sufficient unto the generation are the conditions under which its problems must be discussed. Of old, before the forces of science had girt their strength about them, Vitalism held the field in easy if somewhat lax possession. Then came a period of organised attack. Chemistry and molecular physics had formulated and extended their generalisations and began to urge that the problems of physiology were problems of chemistry and physics-nothing more. There was no vital remainder. Taking their stand on the conservation of energy, they contended that the conception of Vital Force involved the nonproven and improbable appearance of energy without physical or chemical antecedents. This carried conviction among some of our leading physiologists. Professor (Sir John) Burdon Sanderson wrote: "The proof of the non-existence of a special 'vital force' lies in the demonstration of the adequacy of the known sources of energy in the organism to account for the actual day by day expenditure of heat and work." But an answer in due course came from the Vitalists. It was pointed out that the application of a force to a moving body at right angles to its course alters the direction of motion without affecting its amount. The energy remains unchanged. Of such a directive character, it is sometimes urged, may be the application of Vital Force without presenting any phenomena contradictory of the generalisation that, in the operations of nature, energy is nowhere either destroyed or created.
So long as the metaphysical conceptions of Force are carelessly commingled with the generalisations of dynamics as a science, this line of argument may appear to possess a cogency which is in truth fictitious. But what is the basal law of dynamics? That every movement of a part in any material system or configuration, and every state of strain therein, has as its antecedent the assignable nature and distribution of the constituent parts in that system. This is a generalised statement of dynamic fact which quietly ignores (though it does not deny) the existence of Force as the Cause of motion. Granting therefore that a Vital Force is conceivable which alters the direction of motion without producing any change in the amount of energy, the question still remains: Is the movement so produced in accordance with, or is it contradictory to, the basal law of dynamics? For the change of direction of motion is itself a motion, and involves acceleration, though it be unaccompanied by any increase or diminution of energy. If therefore the motion in question is the outcome of the nature and distribution of the constituent parts in a material system of what we have spoken of as a configuration it is a natural movement co-ordinate with other physical movements, and Sir John Burdon Sanderson's contention is in essence valid, as a protest against Vitalism, though it is incompletely stated; if, on the other hand, the motion is not such an outcome, then, though the conservation of energy may still hold its ground, what I have termed the basal law of dynamics cannot. There are movements of material particles which are outside this generalisation. It is questionable, however, whether there are many Vitalists of scientific training who would care to contend for the truth of this conclusion.
In an able address delivered at the meeting of the British Association in 1898, the President of the Chemical Section, Professor Japp, urged that life products have certain optical properties which imply a selective agency of a kind otherwise unknown of a kind which cannot reasonably be attributed to the interaction of forces familiar to the student of chemistry and physics. The phenomena are those known as rotary polarisation. The plane of a beam of polarised light is twisted to left or to right on passing through certain crystalline substances and certain solutions. A solution of racemic acid is inactive or has no effect of this kind. But if it be allowed to crystallise rhombic hemihedral crystals are formed. These are asymmetrical, but some are asymmetrical in one direction, some in another, so that the crystals of one group are like mirror-images of those of the other group. Such crystals are termed enantiomorphs. Now if a number of the crystals of one group are picked out and dissolved, and a number of the crystals of the other group are similarly selected and dissolved, the two solutions thus obtained exhibit rotary polarisation. In the one case the plane is twisted to the right, and in the other case in like degree to the left.
But if, instead of crystallising the original solution, a vegetable "mould," Penicllium, be grown in the solution, and the solution be then filtered, it will be found to exhibit left-handed rotary polarisation. The mould has selected the right-handed moiety of the racemic acid for the purposes of its growth, and a left-handed residuum remains. And this is the outcome of the vital forces of the mould. "I see no escape," says Professor Japp, "from the conclusion that when first life arose, a directive force came into play a force of precisely the same character as that which enables the intelligent operator, by the exercise of will, to select one crystallised enantiomorph and to reject its asymmetric opposite." "No fortuitous concourse of atoms, with all eternity to clash and combine in, could compass the feat of the formation of the first optically active organic compound".