In the first passage certain salient points are strikingly brought out, above all the vast difference between the worlds organic and inorganic; but, next, how much soever a Positivist may be pleased to believe only that which admits of phenomenal verification, it is not every one, especially if given to thought, who would willingly endorse the second paragraph. If we know only what we can verify, many beliefs must needs be abandoned, and amongst them some which have received the almost universal assent of mankind. Knowledge (in the sense of verifiable knowledge) and Belief may appear two widely different things; but it should never be forgotten that we often accept the one as surely as the other. The ancients held that living things arose from the earth at any time, engendered by the warmth of the sun and moisture. Absurd as it may seem, the belief that blue-bottle flies, etc., were a natural result of the decay of meat and other organic matter obtained credence even in comparatively modern times. Redi, an eminent Italian, first demonstrated experimentally the falsehood of this doctrine, and for some time the hypothesis of spontaneous generation appeared to have received a death-blow. And by degrees the conviction that every living thing proceeded from a germ gained strength, and was confirmed by the rapidly extending use of the microscope. Yet in the eighteenth century certain experiments of Needham seemed to establish the fact that in boiled infusions where presumably all germs were destroyed, small Infusoria made their appearance even when means were taken to exclude the entrance of fresh germs. Buffon lent the authority of his great name. These experiments were repeated by the Abbé Spallanzani, who showed by more careful methods the fallacy of the conclusions drawn. A passage in Sir B. Brodie[140] which alludes to these facts may be worth quoting:-- "Crites. Then am I to understand that you would reject altogether the hypothesis of equivocal generation, which supposes that under certain circumstances, even at the present time, particles of inorganic matter are brought together, and so united as to become endowed with organization and life? "Eubulus. The question is one of great interest, and I will refer you to Ergates for an answer, knowing at the same time pretty well what that answer will be. "Ergates. Of course Crites refers to the production of those minute creatures, known by the name of _Infusoria_, in the experiments of Walter Needham, and some others.