This doctrine of vitalism, which held sway for so long, was naturally invoked to explain the origin of life upon the earth, when the advance of astronomy and geology demonstrated a natural evolution for the earth and proved that there must have been a time when no life was possible upon it. The prevalent conception of matter came in at this point and denied altogether any such monstrous doctrine as that the wonderful thing called life could spontaneously arise in the despicable thing called matter. The material of the earth, whether solid, liquid or gaseous, consisted of eternal, unchangeable, and indestructible atoms. These were moved as forces from outside moved them. They had no energy or power of their own. Men simply thought of them as of incredibly minute grains of sand of various shapes and sizes, and it was as impossible to conceive of life being spontaneously generated in a chance heap of inert atoms as to conceive that a heap of grains of sand should organise themselves into a little organism. As for spontaneous generation occurring on the earth to-day, the development of mites from cheese and so forth, that was a very different matter, men must have thought--in so far as they thought at all--since cheese and flesh and so forth were themselves products of life. It is well worth noting that the common doctrine of spontaneous generation was always held in reference to organic materials, such as the slime of the Nile--not the dry sand of the desert. The reader may be inclined to say that men’s beliefs on this subject in the past generation make very confused reading, and indeed, that is true. But the fact is that their beliefs were most confused. The work of Darwin had staggered everybody, and straightforward, systematic, unprejudiced thinking was very nearly impossible in the welter of controversy. Nevertheless, something apparently definite was done. The doctrine of the beginning of life upon the earth was left almost undiscussed, and the accepted notion of the nature of matter--a notion which to us who know radium seems puerile--was left unchallenged in all its falsity. But the work of the great French chemist Pasteur led to a close examination of the belief that humble forms of life are daily produced from lifeless organic materials, and the conclusion was reached that no such spontaneous generation occurs. [Sidenote: Every Living Thing from a Living Thing]