CHAPTER I.
THE DOCTRINE OF VITAL UNITY.
Phenomena common to all living beings—Theory of vital duality—Unity in the formation of immediate principles—Unity in the digestive acts—The common vital fund.
When we ask the various philosophical schools what life is, some show us a chemical retort, and others show us a soul. Whether vitalists or of the mechanical school, these are the adversaries who since philosophy began have vainly contested the possession of the secret of life. We need not concern ourselves with this eternal quarrel. We need not ask Pythagoras, Plato, Aristotle, Hippocrates, Paracelsus, Van Helmont, and Stahl what idea they formed of the vital principle; nor need we probe to the depths the ideas of living nature held by Epicurus, Democritus, Boerhaave, Willis, and Lamettrie; nor need we apply to the iatromechanicians nor to the chemists. We may do better than that. We may ask nature itself.
Phenomena Common to Living Beings.—Nature shows us an infinite number of beings, animal or vegetable, described in ordinary language as living beings. This language implicitly assumes something common to them all, a universal manner of being which belongs to them without distinction, without regard to differences of species, types, or kingdoms. On the other hand, anatomical analysis teaches us that animated beings and plants may be divided into parts ever decreasing in complexity, of which the last and the simplest is the anatomical element, the cell, the microscopic organic unit which, too, is alive. Common opinion suspects that all these beings, whether entire as in the case of animal and vegetable individuals, or fragmentary as in the case of cellular elements, have the same manner of being, and present the same body of common characteristics which rightly gives them this unmistakable title of living beings. Life then essentially would be this manner of being, common to animals, vegetables, and their elements. To seize in isolation these common, necessary, and permanent features, and then to synthetize them into a whole, will be the really scientific method of defining life, and of explaining its nature.
And here then immediately arises a fundamental question which gives one pause, a question of fact which must be solved before we can go further. Is there really a common manner of being in all these things? Are animal life, vegetable life, and the life of the elements or elementary life, all the same? Is there a sum total of characteristics which may define life in general?
The physiologists, following in the steps of Claude Bernard, respond in the affirmative. They accept as valid and convincing the proof given of this vital community by the illustrious experimentalist. However there are some rare exceptions to this universal assent. In this concert of approval there is at least one discordant voice, that of M. F. Le Dantec.[13]
The Doctrine of the Vital Duality of Animals and Plants.—There are, therefore, biologists who, in the domain of theory and in virtue of more or less well-founded conceptions or interpretations, separate elementary life from other vital forms, and thus break the bond of vital unity proclaimed by Claude Bernard. This monistic doctrine at the outset met with other opponents, and that, too, in the domain of facts. But it triumphed over them and became established. We have to deal with scientists like J. B. Dumas and Boussingault, who drew a dividing line between animal life and vegetable life.
But let us in a few words recall to the reader this victorious struggle of the monistic doctrine against the dualism of the two kingdoms. If we consider an animal in action, said the champions of vital dualism, we agree that it feels, moves, breathes, digests, and finally, that it destroys by a real operation of chemical analysis the materials afforded to it by its ambient world. It is in these phenomena that are manifested its activity, its life. Now, added the dualists, plants do not feel, do not move, do not breathe, and do not digest. They build up from immediate principles, by an operation of chemical synthesis, the materials they borrow from the soil which bears them, or from the atmosphere which surrounds them. There is, therefore, nothing in common between the representatives of the two kingdoms if we confine ourselves to the examination of the actual phenomena which take place in them. To find a resemblance between the animal and the vegetable, said the dualists, we must set aside what they do, for they do different, or even contrary things. We must consider whence they come and what they become. Both originate in organisms similar to themselves. They grow, evolve, and generate as they themselves were generated. In other words, while their acts separate plants from animals, their mode of origin and evolution alone bring them together. Such analogies are of no slight importance; but they were neutralized by their dissimilarities, which were exaggerated by the dualistic school.
It is clear that the word life would lose all actual significance to those who would reduce it to the faculty of evolution, and who would separate all its real manifestations in animated beings and in plants. If there are two lives, the one animal and the other vegetable, there are no more; or, what comes to the same thing, there is an infinite number of lives which have nothing in common but the name, or at most, the possession of some secondary characteristics. There are as many of them as there are different beings, for each has its own particular evolution. Here the specific is the negation of the general and it destroys it instead of being subordinate to it. The principle of life becomes for each being something as individual as its own evolution. And this, if we think it out, is how the philosophers look at life, and it is the real reason of their disagreement with the physiological school.
Proof of the Monistic Theory.—On the other hand, under the disguise of living forms, the physiologist recognizes the existence of an identical basis. His trained ear marks amid the overcharged instrumentation of the vital work the recognizable undertones of a constant theme. It was the work of Claude Bernard to bring this common basis to light. He shows that plants live as animals do, that they breathe, digest, have sensory reactions, move essentially like animals, destroy and build up in the same manner the immediate chemical principles. For that purpose it was necessary to pass in review, examining them from their foundation and distinguishing the essential from the secondary, the different vital manifestations—digestion, respiration, sensibility, motility, and nutrition. This is what Claude Bernard did in his work Sur les Phénomènes de la vie communs aux animaux et aux plantes. We need only to sketch in broad outline the characteristic features of his lengthy demonstration.