SPONTANEOUS GENERATION and PRO TOGENESIS. The doctrine that different forms of life, especially the lower, have arisen by phy sico-chemical agencies from inorganic substances. This view prevailed from ancient time* until after the middle of the seventeenth century, and as late as 1842 Weeks maintained that mites (Aearus) were spontaneously generated in "sev eral solutions under eleetrieal influence." In 18a9 Pouchet, in his lleterogt'aie, revived the sub ject, and in 1871 Bastian maintained that bac teria and toruke were developed at the present day in certain fluids containing organic matter by laws similar• to those by which crystals arise, or by what he calls 'archebiosis.' In Difiu Redi disproved the prevailing notion that the maggots of Ilies were generated in putre fying meat, by covering similar pieces of meat with fine gauze, and keeping away the blow-Ilies. Ile thus demonstrated that the inagots grew from and that there was "no life without antecedent life." About a century and a half ago Needham 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 ( 708) to make more careful experiments. 11e 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. Schulze and Schwalm in 183G made further experiments. They care
fully boiled their infusions, and then sup plied air; but they made it first pass through red hot tubes, so that any germs present in it would be burned. Under these conditions no infuso•ia appeared. Then the discovery was made by Ca gniard de la Tour that fermentation, like putre faction, is always accompanied by the presence of microscopic organisms. In 1854-a9 Schroeder and Nisch invented the screen of cotton-wool now used for plugging the openings of tubes, which kept nut 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, 1 862). On sowing these particles in suitable sterilized infusions he raised from them micro scopic organisms. Germs like these were after wards shown by Cohn to be low plants to which he gave the name 'bacterium.' Filially Tyndall, in ISO. 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.