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to whether it be internal or external to an organism, is, in other words, to affirm a miracle. If this is weighed against the physical view, "which in its perfection reduces every organic process to a problem of pure mechanics," it may be done in the certainly impartial words of the naturalist just quoted: "I am of opinion that the mechanical view of organic life is demonstrated only when all the motions in an organism are shown to be the effects of forces, which at other times also are inherent in the atoms. But similarly I should regard the vitalistic view as proved, if in any case a particular motion actually observed to take place in an organism were shown to be mechanically impossible. At present, neither is to be thought of. Nevertheless, if a decision must be made without full proof, I provisionally profess myself unequivocally in favour of the mechanical view. Not only does it recommend itself à priori by its superior probability and simplicity, but the progress of scientific development raises it almost to a certainty. When it is seen how certain phenomena-such as the evolution of animal heat, which it was formerly believed could be explained only by vital force-are now ascribed, even by those who in general assume the existence of a special vital force, to the universally active forces of the material particles, we find ourselves almost forced to the conviction that by degrees all the phenomena of life will become susceptible of mechanical explanation."
For the elucidation of the example just given of animal heat, let us observe that modern physics have learnt to know heat as a peculiar mode of motion. The motion of the hammer as it falls upon the anvil is not lost, but
is transformed into the atomic motion of the places struck, a motion, invisible, it is true, but sensible as heat. But likewise the combination of the particle of oxygen introduced into the animal body by the respiration, with the un-oxygenated constituents of the blood, is a motion subject to computation, and manifesting itself as oxydation, combustion, or the evolution of animal heat. This chemical act of combustion keeps the animal steam-engine in motion.
In this way, by the application of mechanical principles, modern physiology has traced to their causes a great number of organic processes, and the phantom of vital force, which formerly reigned paramount over the whole intestinal canal, incited the glandular cells and the muscular fibres to their offices, and glided along the nerves, now scarcely knows where to breed disturbance.
Thus the investigation of nature does not shrink from enrolling life and the processes of life in the world of the comprehensible. We are foiled only at the conception of matter and force. But we are much further advanced than Schopenhauer and his adherents, who for the idea of Force substitute that of Will; for we have analyzed into their several self-conditioned momenta a multitude of processes, which the word "Will," incomprehensible in itself, is supposed to explain in their totality; and much further also than the fashionable philosopher of the day, von Hartman, who regales us with the agency of the "unknown" in the domain of the organic world.
"And yet," Dubois-Reymond thus formulates another limit, "a new incomprehensible appears in the shape of consciousness even in its lowest form, the sensation of desire and aversion. It is, once for all, incomprehen
sible how, to a mass of molecules of nitrogen, oxygen, hydrogen, carbon, phosphorus, and so on, it can be otherwise than indifferent how they lie or move; here, therefore, is the other limit to the knowledge of natural science. Even the mind imagined by Laplace cannot go beyond this, to say nothing of our own. Whether the two limits to natural science are not, perchance, identical, it is, moreover, impossible to determine."
In these last words the possibility is indicated that consciousness may be an attribute of matter, or may appertain to the nature of the atoms. And we may add, that the attempt has of late been repeatedly made to generalize the sensory process, and to demonstrate it to be the universal characteristic of matter, as by von Zöllner, in his work on the Nature of Comets, which has created such a justifiable sensation. He holds that, if by means of delicately-formed organs of sensation it were possible to observe the molecular motions in a crystal mechanically injured in any part, it could not be unconditionally denied that the motions, hereby excited, take place absolutely without any simultaneous excitement of sensation. We must either renounce the possibility of comprehending the phenomenon of sensation in the organism, or "hypothetically add to the universal attributes of nature, one which would cause the simplest and most elementary operations of nature to be combined, in the same ratio, with a process of sensation."
It might be imagined that reflections of this kind. would lead to the delusive abysses of speculation; but if, still speaking only of organisms, we descend from the manifestations elicited by sensations of desire and
aversion in the higher consciousness of man and of the superior animals, till we see all reaction to external excitation dwindle into the scarce perceptible motions of the simplest protoplasmic animalculæ, it is evident that there can be no question here of either consciousness or will. We cannot then separate the idea of those sensations of desire and aversion, by which motions are excited, from the elementary attributes of matter, as we are wont to do with regard to the higher animals.5
In precisely the same sense, it was said some years ago by one of the most talented investigators of language-Lazarus Geiger, now unfortunately deceased: 6 "But how is it, if further down, below the world of nerves, a sensation should exist which we are not capable of understanding? And it probably must be so. For as a body that we feel could not exist unless it consisted of atoms that we do not feel, and as we could not see a motion were it not accompanied by waves of light which we do not see, neither could a complex living being experience a sensation strong enough for us to feel it also, in consequence of the motion by which it is manifested, if something similar, though far weaker and imperceptible to us, did not occur in the elements, that is to say, in the atoms. If we only consider that we are as little capable of knowing that the falling stone feels nothing, as that it does feel; it is fully open to us to decide, in accordance with the greatest probability, that the world is susceptible of explanation."
We have examined the limits which the investigation of nature has prescribed for itself. The organic world,
far from rearing itself before us as an incomprehensible entity, invites us to fathom its nature, and promises to reflect fresh light upon the inanimate world.
We must now pass in review a great portion of animate nature, and shall then arrive at the same conclusion as the linguistic inquirer, to whom we again quote his words-" it became, on historic grounds, incontrovertibly certain that man has risen from a lower, an animal grade,"