I08 THE CONCEPTION OF LIFE 



generation from the meat. Francesco Redi's famous experi- 

 ments brought the first proof that the insects arise only when 

 insect eggs are laid in the meat. For a still longer time it 

 was considered possible that the simplest organisms, bacteria, 

 etc., could be formed by spontaneous generation. The 

 experiments of Pasteur, made not many years ago, brought 

 the final proof that this also is impossible. On Pasteur's 

 discovery is based the antiseptic treatment of the surgeon, 

 which has for its object simply to prevent the entrance of the 

 microscopic germs which cause sepsis. We must regard it 

 as an assured conclusion of biology that spontaneous genera- 

 tion has never been observed, and many naturalists incline 

 to assert that it never will be observed by us. ' 



Thus we come back to the question, where does the Uving 

 substance come from? Helmholtz^^ and, following him, 

 Arrhenius have defended a h)^othesis according to which 

 life reached this earth from outside. This hypothesis assumes 

 the occurrence of very small living germs, about of the size of 

 the smallest individual germs known to us as occurring on the 

 earth, which are driven hither and thither in space, and may 

 accidentally hit the earth, or which perhaps are brought on 

 meteorites, or, according to the h37pothesis advanced by 

 Arrhenius, by the beats of waves of light. The hjrpothesis is 

 bold and interesting. If it is correct, the possibiUty exists 

 of our receiving organisms which differ from aU species hith- 

 erto occurring on the earth, and which therefore might initiate 

 a new evolution of living beings. But even if we assume the 

 correctness of this hypothesis, it still offers no answer to our 

 question, because it assumes the previous existence of living 

 substance. Alongside this theory occurs a new hj^othesis of 

 spontaneous generation. This second hypothesis is, so to 

 speak, a side product of the doctrine of evolution. After the 



