Page:The New International Encyclopædia 1st ed. v. 18.djvu/539

* SPONTANEOUS GENEBATION. 463 SPONTANEOUS GENERATION. sico-chemical agencies ffom inorganic substances. This view prevailed from ancient times until after the middle of the seventeenth ceiilinT, and as late as 1842 Weeks maintained that mites (.cariis) were spontaneoush' generated in "sev- eral solutions under electrical inlluenee." In 1859 Poucliet, in his Heterogenic, revived the sub- ject, and in 1871 Bastian maintained that bac- teria and tonihie were developed at the present daj' in certain fluids containing organic matter by laws similar to those b.v which crystals arise, or by what he calls 'archebiosis.' In 1G60 Redi disproved the prevailing notion that the maggots of flies were generated in ])utre- fying meat, liy covering similar pieces of meat with fine gauze, and keeping away the blow-llies. He thus demonstrated that the njaggots grew from eggs, and that there was "no life without antecedent life." About a century and a half ago Xeedham experimented by boiling and corking flasks of water containing infusoria, but in every case animalcules appeared after a longer or shorter period. This led Spallanzani (1708) to make more careful experiments. He boiled in- fusions longer, and instead of simply corking, fused the necks of his flasks. The result was that the infusions remained entirely free from living organisms. Sehulze and Schwann in 1836 made further experiments. They care- fully lioiled their infusions, and then sup- plied air; but they made it first pass through red- hot tubeSj so that any germs present in it would be burned. Under these conditions no infusoria appeared. Then the discovery was made by Ca- gniard de la Tour that fermentation, like putre- faction, is always accompanied liy the presence of microscopic organisms. In 1854-59 Schroeder and Puseh invented the screen of cotton-wool now used for plugging the openings of tubes, which kept out the germs, and it was thus found that the cause of putrefaction and fermentation, and the origin of the living forms accompanying these processes, must be microscopic particles existing in the air. The next step was taken by Pasteur {On the Organized Particles Existing in the Air, 18ti2). On sowing these particles in suitable sterilized infusions he raised from them mioro- Bcopic organisms. Germs like these were after- wards sliown by Cohn to be low jdants to which he gave the name ■bacterium.' Finally Tyndall, in 1869, by passing a beam of light through the air in a box, showed that whenever dust was pres- ent the putrefaction occurred sooner or later; when it was absent it did not. The result of these experiments and conclusions is that the view that spontaneous generation takes place at the present day has been entirely discarded. Spontaneous Geneb.tion (Protogenesls) Necessary to Account for the Beginnincs of Life. Some of those who, like Wyman, made obser- vations disproving its occurrence at the jiresent day, yet supposed that in the beginning the first living organisms probably arose from inorganic matter, through the action of unknown physico- chemical processes. In 1868 Herbert Spencer, while rejecting the ancient doctrine of spon- taneous generation, stated his belief that the formation of organic matter and the evolution of life in its lowest forms "took jilace at a time when the heat of the earth's surface was falling through ranges of temperature at which the higher organic compounds are unstable." He conceived that the molding of such organic mat- ter must have begun with jiortioiis of protoplasm, more minute, more iiulelinite. and more incon- stant in their characters than the lowest rhizo- pods, or even the Protogenes of llacckel. With this view biologists are now in agreement. It is evident that the earliest living organism appeared when the temjierature of the eartli's crust and of the air and sea approached that which it is now; the earth's climate proliably ex- ceeded in temperature that of the ]U'esent torrid zone; the sea may have been less saline; but wo know that at present exceedingly few plants and animals can live in hot springs; that there is no life in our geysers, and, judging from analogy, the earth's surface must have been nearly as it is now when the first bit of animated protoplasm came into being. When the earth had assumed its present shape, with its incipient continents, and the oceans lying in their basins, the period arrived when the con- ditions for the appearance of life became favor- able, and at this critical moment the protoplasmic sulistance probably came into being. The chemi- cal compounds giving origin to it were far more abundant, and the physical and chemical con- ditions more favorable. The origin of protoplasm was probably the re- sult of a combination of circumstances which cer- tainly never occurred before in the hist<iry of our planet, and which has never happened since. The phenomenon of protogenesis, after taking place once for all, could never have again occurred. Such is the nature of cell-division, of sexual re- production, of growth, and of heredity, that it would be contrary to the course of nature to sup- pose that it was ever afterwards necessary for it to again occur. After protoplasm appeared, the earth and ocean probably became too cool to sup- ply a sufficiently high temperature, or chemical compounds of the right degree of stability to form protoplasm. First Beginnings of Life. To account for the beginnings of life we have been compelled to im- agine the creation of a primordial microscopic bit of protoplasm. In shape it was drop-like, spherical or oval, its form being due to gravity, as the primary form of all living beings tends by the action of gravity to be round or ovate. This primordial being had the power of ab- sorbing and digesting food, or the protoplasmic materials round it, and hence of growing: it was contractile and eould move automatically, and thus it was adapted for moving through the wa- ter, sending out from its body rootlike exten- sions or pseudopodia to aid in seizing its food and in locomotion. A single 'chance' germ (though in nature there is no such thing as chance) would have been sutTieient. Such a primordial cell or sphere of protoplasm, by the simple process of self-division, even if not far enough advanced in organization to have a nucleus, may have multiplied itself, and in a few hours even become the parent of thousands of young, while the lapse of a few days would enable it to give birth to millions. These primordial beings were plastic. .'Iready the earth's surface varied, if not in relative dis- tribution of land and sea. in depth, specific grav- ity, density, light, and shade, in the nature of the bottom of the primeval sea, and in chemi- cal constitution and other physical features.