This law derived from the nature of spontaneous generation has very recently attained its complete empirical confirmation, in that the microscope has uniformly revealed, where one had formerly supposed spontaneous generation, sexual generation, and at the present day no single case of actual spontaneous generation has been observed, notwithstanding that the microscope has very carefully swept the province of minute life in all directions.

I do not at all dispute that the possibility is at any moment open of establishing spontaneous generation at the present time; I even concede that the negative proof, that now there can be no spontaneous generation, must always remain for experientialism an impossibility; but nevertheless we may well assume that an assertion, in which theory and empirical observation agree, has a considerable probability in its favour.

For the reader not conversant with the interesting facts relating to this subject I add a short notice of the same.

Aristotle believed that most of the lower animals arose by spontaneous generation. A few centuries ago spontaneous generation was assumed for intestinal worms and infusoria, although for a long time voices were heard suggesting the possible overlooking of parental germs. First the modes of immigration and different states of the intestinal worms were scientifically established; then it was shown that infusions boiled for more than five hours, which came in contact only with heated air, gave rise to no organisms. The advocates of spontaneous generation, however, justly replied that the heating of the air must also destroy the capability of the production of organisms.

Schröder and Dusch first showed that a plug of cotton twenty inches in length filtrates the air in such a way that it allows no organisms to arise.-Pasteur examined the germs floating in the air by catching them in guncotton and dissolving the latter in ether and alcohol.

He found the same to answer in all respects to the otherwise familiar germs of the lowest animals. He also positively proved, that they are the cause of the development of organisms in the infusions, by introducing along with the heated air a small plug of cotton containing germs, and the organisms always appeared, as if the air had had free access. Pasteur even compared by an ingenious. method the relative quantities of the germs contained in the air at different localities. Recently Crace-Calvert ascertained by his exact investigations that temperatures of 100° C. do not essentially affect the minute organisms in question;1 that at 149° C. only those which develop in solution of gelatine become incapable of germination, but that for the destruction of the germinal power of the organisms which develop in the other experimental solutions a temperature of 204° C. is requisite. Accordingly the assumption of a spontaneous generation in infusions. has been scientifically set at rest once for all.

I will mention one more case, the origination of Monas amyli. A swarm of unicellular infusoria was seen to arise in starch granules, and it was thought that spontaneous generation was being witnessed. But when the history of these creatures was traced farther, one saw them become liberated on the final disruption of the starch granule, each seek a fresh starch granule and completely cover it, expanding after the fashion of the Amœbæ. This thin little skin on the surface of the grain, the animal, which had swallowed the corn, as it were, and now slowly digested it in layers, had previously escaped observation. Now, of course, the origin of the brood was recognised as endogenous increase.

The law of reproduction is so universal in Nature, that not only no case of the parentless origin of an animal or a plant is known to us, but even not a case of the parentless origin of a cell in an existing organism.

1 Those capable of resisting higher temperatures are, according to Ferd. Cohn, the germs of Penicillium, whilst

according to the same investigator the germs of Bacterium are killed already at 80° C.

If spontaneous generation could occur anywhere, one would certainly expect to find it in a spontaneous arising of cells in the juices of an existing organism, where both the temperature and the chemical composition of organic matter affords the most favourable suppositions conceivable; but in vain. Even within the organism cell only arises from cell.

All sober-minded naturalists allow that, from the negative results of the most careful investigations with our present perfect instruments, there results a high probability for the supposition that spontaneous generation does not take place at the present day. From the probability of this assumption one must however regressively conclude that the spontaneous generation even of the simplest Protozoa must be none so easy and simple an affair, and that for the re-establishment of the same quite other conditions are required than a mere mechanical individuation of existing protein substances. Were it not so, the spontaneous generation of Protozoa from protein-containing fluids must be observable under the microscope with the proper temperature, illumination, ozone-containing air, &c.; but even supposing a case of successful experiment, it would still never appear credible that such a Moner, which always belongs to a well-defined species in virtue of its mode of nutrition and propagation, could arise and functionally persist by the mere play of inorganic atomic forces (comp. also pp. 212, 213 and 291293), without psychical influences from the Unconscious ideally regulating the mode of this activity.

X.

THE ASCENDING EVOLUTION OF ORGANIC LIFE

ON THE EARTH.

WE have in the last chapter shown the probability of the assertion that the Unconscious expended its energy in spontaneous generation only as long as was necessary, i.e., until reproduction could be substituted for it. From the same first principle of Nature of the greatest possible saving of energy directly follows also the other proposition, presupposed as self-evident in the preceding considerations, that spontaneous generation, i.e., a direct production from unorganised matter, can only have reference to the very simplest forms of organic life; that, on the contrary, for the genesis of higher life-forms the Unconscious will by no means choose the course of direct production, so difficult for the simplest beings, but a mode of origination effected by gradual stages. Not that I would maintain the absolute impossibility of the direct original creation of a higher animal; on the contrary, I have always maintained the Will can do what it will, if it only wills with sufficient intensity to overcome the opposing acts of will. Not that I would deny the theoretic possibility that even within the range of the inorganic laws of Nature, at certain moments of terrestrial development, the Unconscious could have set up a direct spontaneous generation of higher animals; to presume to decide the point were folly. Only this much I assert, that a direct spontaneous generation of higher organisms would have required an enormous application of force, an expenditure of energy

which would have infinitely exceeded that requisite for the original creation of the simplest cell; that therefore the infallibly logical in the Unconscious, agreeably to the principle of the attainment of all ends with the least possible expenditure of energy, could not but prefer to the spontaneous generation of higher organisms a mode. of production effected by many transitional stages, each of which, besides paving the way for higher beings, served in addition other and independent ends, and at the same time was attainable with a relatively trifling expenditure of force by means of a plastic principle of descent.

If we ask plainly, what would be needed for the spontaneous generation of a higher organism? the answer is: in the first instance, organic substances of not too low chemical composition in sufficient quantity and sufficient concentration. Where, however, are these more easily to be found. than in an already existing inferior organism? In any case, therefore, the direct transformation of an already existing inferior organism into a higher one (e.g., of a worm into a fish) would offer fewer difficulties than the spontaneous generation of the latter without the assistance of an existing organism. But here too the difficulties would always be still so great, that an enormous application of the energy of the Unconscious would be required to surmount them; for the already established forms and elaborated organs of the lower organism must for the most part be first annihilated, in order to give place to the corresponding forms and organs of the higher being. This not inconsiderable negative work, of previously annihilating what had been created in the embryonic development of the lower organism, is manifestly altogether avoided if the metamorphosis begins at stages of development so early that these specific forms and organs of the lower stage are never brought to perfection, but in lieu thereof at once those of the higher grade. Strictly then one can only speak in an ideal sense of a metamorphosis, for only the ideal type, which proceeded according to the ordinary course of de