And seeks, with ebbing tide, his ancient bed,
The fat manure with heavenly fire is warmed,
And crusted creatures, as in wombs, are formed;
These, when they turn the glebe, the peasants find;
Some rude, and yet unfinished in their kind.
Short of their limbs, a lame, imperfect birth;
One half alive, and one of lifeless earth."
Crude ideas of this kind prevailed universally until the seventeenth century. The celebrated physiologist, Dr. William Harvey, the discoverer of the circulation of the blood, has the credit of first propounding the modern view expressed in the maxim "Omne vivum ex vivo," which being interpreted signifies, "No life without antecedent life." He maintained that all living beings proceed from eggs; but exactly what he meant by "eggs," that is, whether they were always derived from parental organisms, or might originate in some other way, is considered uncertain.
The first distinct announcement of the doctrine that all living matter has sprung from preëxisting living matter, was made by Francesco Redi, an Italian physician, who published his views just two hundred and four years ago. His position is thus stated by Prof. Huxley: "Here are dead animals, or pieces of meat; I expose them to the air in hot weather, and in a few days they swarm with maggots. You tell me that these are generated in the dead flesh; but, if I put similar bodies, while quite fresh, into a jar, and tie some fine gauze over the top of the jar, not a maggot makes its appearance, while the dead substances, nevertheless, putrefy just in the same way as before. It is obvious, therefore, that the maggots are not generated by the corruption of the meat, and that the cause of their formation must be a something which is kept away by gauze. But gauze will not keep away aëriform bodies or fluids. This something must, therefore, exist in the form of solid particles too big to get through the gauze. Nor is one left long in doubt what these solid particles are; for the blow-flies, attracted by the odor of the meat, swarm round the vessel, and urged by a powerful but in this case misleading instinct, lay eggs out of which maggots are immediately hatched upon the gauze. The conclusion, therefore, is unavoidable: the maggots are not generated by the meat, but the eggs which give rise to them are brought through the air by the flies."
These experiments were unanswerable; but the doctrine of spontaneous generation had been too long and firmly believed, to be surrendered merely because of the demonstrated falsity of its grounds. It was held to have the sanction of the Bible, which affirmed that bees were generated from the carcass of a dead lion: Dr. Redi was therefore called upon to defend himself against the charge of impugning Scripture authority.