Thus we are able to study this crystalline species of glycerine and to determine with precision the conditions of its continued existence. It has been shown that it does not resist a temperature of 18°, so that if precautions were not taken to preserve it, a single summer would suffice to annihilate all the crystalline individuals existing on the surface of the globe, and thus the species would be extinguished.
Possible Extinction of a Crystalline Species.—As these crystals melt at 18°, this temperature represents the point of fusion of solid glycerine or the point of solidification of liquid glycerine. But the liquor does not solidify at all if its temperature falls below 18° C., as we well know, for it is at that temperature we use it. Nor does it solidify at zero, nor even at 18° below zero; at 20°, for instance, it merely thickens and becomes pasty. We only know glycerine, then, in a state of superfusion, a fact which chemists have not learned without amazement. Under these conditions, so analogous to the appearance of a living species, to its unlimited propagation and to its extinction, the mineral world offers a quite faithful counterpart to the animal world. The living body illustrates here the history of the brute body and facilitates its exposition. Inversely, the brute body in its turn throws remarkable light on the subject of the living body, and on one of the most serious problems relative to its origin, that of spontaneous generation.
Conclusion.—These facts lead to one conclusion. Until the concourse of propitious circumstances favourable to their spontaneous generation was brought about, crystals were obtained only by filiation. Until the discovery of electro-magnetism, magnets were made only by filiation, by means of the simple or double application of a pre-existing magnet. Before the discovery which fable attributes to Prometheus, every new fire was produced only by means of a spark from a pre-existing fire. We are at the same historical stage as regards the living world, and that is why, up to the present, there has never been formed a single particle of living matter except by filiation, except by the intervention of a pre-existing living organism.
BOOK V.
SENESCENCE AND DEATH.
Chap. I. The different points of view from which death may be regarded.—Chap. II. Constitution of the organisms—Partial death—Collective death.—Chap. III. Physical and chemical characteristics of cellular death—Necrobiosis.— Chap. IV. Apparent perennity of complex individuals.—Chap. V. Immortality of the protozoa and of slightly differentiated cells.
We grow old and we die. We see the beings which surround us grow old and disappear. At first we see no exceptions to this inexorable law, and we consider it as a universal and inevitable law of nature. But is this generalization well founded? Is it true that no being can escape the cruel fate of old age and death, to which we and all the representatives of the higher animality are exposed? Or, on the other hand, are any beings immortal? Biology answers that, in fact, some beings are immortal. There are beings to whose life no law assigns a limit, and they are the simplest, the least differentiated and the least perfect. Death thus appears to be a singular privilege attached to organic superiority, the ransom paid for a masterly complexity. Above these elementary, monocellular, undifferentiated beings, which are protected from mortality, we find others, higher in their organization, which are exposed to it, but with whom death seems but an accident, avoidable in principle if not in fact. The anatomical elements of this higher animal are a case in point. Flourens once tried to persuade us that the threshold of old age might be made to recede considerably, and there are biologists in the present day who give us some glimpse of a kind of vague immortality. We may, therefore, ask our readers to follow us in our examination of these re-opened if not novel questions, and we shall explain the views of contemporary physiology as to the nature of death, its causes, its mechanisms, and its signs.
CHAPTER I.
VARIOUS WAYS OF REGARDING DEATH.
Different meanings of the word death—Physiological distinction between elementary and general death—Non-scientific opinions—The ordinary point of view—Medical point of view.—The signs of death are prognostic signs.
Different Meanings of the Word Death.—An English philosopher has asserted that the word we translate by “cause” has no less than sixty-four different meanings in Plato and forty-eight in Aristotle. The word “death” has not so many meanings in modern languages, but still it has many. Sometimes it indicates an action which is taking place, the action of dying, and sometimes a state, the state which succeeds the action of dying. The phenomena it connotes are in the eyes of many biologists quite different, according as we watch them in an animal of complex organization, or on the other hand, in monocellular beings, protozoa and protophytes.
Physiological Distinction between Elementary Death and General Death.—We distinguish the death of the anatomical elements, elementary death, from the death of the individual regarded as a whole, general death. Hence we recognize an apparent death, which is an incomplete and temporary suspension of the phenomena of vitality, and a real death, which is a final and total arrest of these phenomena. When we consider it in its essential nature (assumed, but not known) we look on it as the contrary of life, as did the Encyclopædia, Cuvier, and Bichat; or we regard it with others either as the consequence of life, or simply as the end of life.