The theory of biogenesis had accumulated so…

In 1861, Louis Pasteur had performed a series of experiments that demonstrated that organisms such as bacteria and fungi do not spontaneously appear in sterile, nutrient-rich media, but only invade them from outside.

Pasteur himself remarks, after a definitive finding in 1864, "Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment." (Oparin, Aleksandr I. (1953). Origin of Life. Dover Publications, New York. p. 196.)