Imágenes de páginas
PDF
EPUB

somewhat altered, becomes the substance of the animal. First and last, from the lowest vegetable to the highest animal, wherever there is life there must be protoplasm.

Should you wish to learn more about it, you may be told that protoplasm contains oxygen, hydrogen, nitrogen, and carbon combined in a very complicated manner : the meaning of which may be illustrated by a common substance like sugar, let us say. The chemical symbol for cane-sugar is C12,H1,011, which signifies that when 12 equivalents of carbon, 11 of hydrogen, and 11 of oxygen combine, the product is sugar. Added together, we have 34 simple atoms, which may be arranged in a thousand different ways. With every alteration in the position of any single one of these atoms, as Liebig tells us, “the compound atom ceases to be an atom of sugar, since the properties belonging to it change with every alteration in the arrangement of the constituent atoms." In protoplasm we have an additional element in nitrogen, not to mention a dash of sulphur and of phosphorus. When, therefore, one is informed that an atom of protoplasm contains at least goo elementary atoms instead of 34, the complexity of combination, though not picturable, may be said to be faintly adumbrated to the mind. When one is further informed that nitrogen has a remarkable propensity to set a hair-trigger to every substance with which it combines; that the now famous dynamite owes its extreme instability or explosive tendency to the presence of nitrogen; that fish, meat, and especially eggs, speedily decompose on account of the nitrogen in the albumen, &c.-it becomes evident that the great unlikeness between the combined units in so highly compound an atom as one of protoplasm must, when subjected to disturbing forces, facilitate the differentiation essential to development, and ultimately promote the changes essential to high organisation. With these prefatory remarks we may attack the question of Spontaneous Generation.

1. Was life originally evolved from inorganic matter? 2. Is life now evolved from inorganic matter, or is it always propagated from living substances? With regard to the first query, we can but speculate. Still (setting apart metaphysical considerations for future discussion, and treating the subject entirely from the realistic point of view), when we reflect that the only physical difference between organic and inorganic compounds is one of higher or lower multiples in elements which are common to both; when we reflect how ambiguous are the lowest phenomena of life; when we reflect on the absolute dependence of its highest manifestations on physical conditions; lastly, when we think of our ignorance and proneness to be carried away by imagination; it is difficult to resist the conclusion that the apparent beginning of life is as natural as its apparent end.

Whether, as Oken, Lamarck, Lewis, Häckel, and many others thought and think, life is incessantly being generated by the formation of its appropriate matter, is beyond the reach of observation. Many conditions may possibly be requisite to its commencement which no longer exist upon our planet. Moreover, the supply of life, or at least the germs of life, are so astoundingly abundant, that there would not seem to be sufficient reason for further creation. Though, to be sure, this argument is not worth much, seeing that our notions of economy are no guide to nature.

There can be no a priori improbability in the way of artificial generation, supposing this to mean no more than the artificial combination of that which is already fitted for the purpose. Whether even this has ever been achieved is quite another affair. In ancient times belief in spontaneous generation seems to have been universal. Nor was this creed much disturbed till the end of the seventeenth century, when Redi, by means of some very simple experiments, convinced the scientific world that instead of putrefaction engendering life, it was life that engendered putrefaction; in other words, that the life within the putrefying substance comes from life without.

Redi's inferences were greatly strengthened by the eminent microscopists of the eighteenth century. By aid of their improved instruments they discovered that living organisms, though invisible to the naked eye, swarm on every side of us. According to Leuwenhoek, a single drop of stagnant water contains five hundred millions of living organisms. What is true of water in the ditch, is true of broth in the kitchen,-if this also be left for a few days exposed to the ordinary air. All vegetable and animal infusions are subject to a similar change. Where does the life come from? If from antecedent life, as Redi had declared, then it must either be from living germs already in the infusion, or else from such germs floating in the air.

The test, now so familiar to us, was applied by Needham. He boiled the infusions to destroy their living contents, and then sealed his flasks to prevent the entrance of life from without. The result was that, animalcules appeared in spite of the ordeal; and Needham declared for spontaneous generation. Towards the end of the last century Spallanzani, dissatisfied with Needham's experiments, renewed them with care, and with results exactly opposite to Needham's. The inference was that life must come of life, and that its germs were contained in the air. During the present century countless trials have supported this conclusion. When no air is admitted to the boiled infusions but such as has been calcined by passing through red-hot tubes or purified by sulphuric acid, no life appears. When the air is merely filtered by cottonwool, no life appears. Even when the neck of the flask is bent downwards, so that the germs cannot fall upwards, no life appears. If, on the other hand, the air we breathe is admitted, as we breathe it, uncalcined and unfiltered, these same sterilised fluids in a few days become clouded with living beings.

Some twenty years ago, M. Pouchet revived the old dispute by announcing his success in artificial generation. This again brought great experimenters like Pasteur and

Tyndall into the field. The labours of these two finished experts were rewarded with success of another kind. They succeeded in destroying bacterial life, and effectually excluded its existence from infusions most favourable to its development. But the advocates of spontaneous generation were not yet convinced. Dr. Bastian wrote and lectured energetically in its support. He did not doubt the fact that the air contains some germs of living organisms, and that the admission of these into suitable fluids would initiate fermentation or putrefaction.

But his reply to Dr. Tyndall came to this : After boiling and sealing up the infusions, my flasks swarm with bacteria ; and you admit that some of yours do the same. What justifies the assumption that these bacteria or their germs can only be accounted for by supposing them to have survived the boiling ? What present warrant is there for supposing that a naked, or almost naked, speck of protoplasm can withstand four, six, or eight hours' boiling ?2 Dr. Bastian thinks there is none. Besides, he argues, admitting the possibility of imperfection in the experiments—admitting the possibility of contaminating air having reached the infusion, how does the germ-theorist know that that particular air contained living germs ? How does he know that life in these instances was not initiated by “organic particles and fragments resulting from the breaking up of previous living matter of various kinds ?” I don't believe bacteria have any germs at all. The assumption that they have is no better than a guess to suit a foregone conclusion. “In the present state of the evidence bearing upon the subject, I regard the hypothesis of spontaneous generation as the most logical and consistent interpretation of the facts which are at present known."

1 The name bacteria is given to Some high authorities have pro. the smallest known organisms on nounced them to be vegetables ; but account of thestaff-like form of many they cannot properly be classed of them. They vary in size and either as plants or animals. shape, some of them being globular. 2 Nineteenth Century, Feb. 1878.

1. What is the death-point of living matter, or what amount of boiling can it resist ? 2. What does the air contain? These are the two minor issues upon which the main problem turns.

The death-point of living matter, unfortunately for Dr. Bastian's argument, is at present undetermined. Desiccation before entering the infusion, an oily surface, or other unknown causes, may prevent contact with the boiling fluid.

A germ may “pass unwetted and unscathed through sulphuric acid, and in like manner it may escape destruction by a heated liquid. But, according to Professor Tyndall, no infusion can withstand discontinuous heating. If the germs be killed in the order of their resistance, three minutes is “found sufficient to accomplish what three hundred minutes continuous boiling failed to accomplish.” As to naked bacteria, Professor Tyndall ignores their existence. It is true that here and there an experimental flask does contain life; a hundred and thirty such were submitted to the Royal Society in January 1876. “In one flask, and in one only, a small mycelium was discovered.”i “In this flask, and in it only, a small orifice was discovered through which the infusion could be projected, and by which the germinal matter of the air had had access to the flask.” With respect to the existence of bacterial germs, the Bacillus subtilis of hay and the Bacillus anthracis of splenic fever are known to propagate themselves by spores “which may be rendered as plain to the eye of the microscopist as peas in a pod.”

The only debatable ground left as a footing for the heterogenist seems to be on the needle's point of his organic débris. To this hypothesis there are two replies. If the debris is dead, is it more probable that it should engender life in the lifeless infusion, than that the denied living germs should do so? If the débris is not dead, there is no beginning of life. Strictly speaking, spontaneous generation ought to have

1 Nineteenth Century, March 1878.

« AnteriorContinuar »