ORIGIN OF LIFE 



221 



the establishment of this conclusion was Pasteur. His masterly 

 and comprehensive work was not only convincing and final, but 

 it also demonstrated the source of the life that so rapidly appeared 

 in infusions that are exposed to the air. It is the air. A consider- 

 able part of so-called dust is made up of 

 microorganisms in a dormant state ready 

 to resume active life when moisture and 

 other suitable conditions are encountered. 

 Furthermore, these organisms are not the 

 result, but the cause of 

 decay — their own ac- 

 t i v i t i e s bring about 

 chemical changes: putre- 

 faction, fermentation, 

 and, in the bodies of 



Fig. 152. — Flask used by Pasteur in his ex- 

 periments on spontaneous generation. After 

 higher organisms dis- * ne contents were poured in, the top of the 



flask was sealed. The opening at the end was 

 sealed against the entrance of germs, but not 

 oxygen, etc., by the water of condensation 

 that accumulated at the bend. Life did not 

 develop in the flask. 



ease. And this is amply 



attested by the methods 



now universally used in 



food preservation and 



aseptic surgery — to mention but two instances. (Figs. 152, 



153, 278). 



But, though highly improbable, of course it is not impossible 

 that simple life is even at the present time arising spontaneously 

 under special environmental conditions, perhaps in the ocean 

 depths, though unable to come to fruition in competition with 

 existing highly specialized protoplasm of ancient pedigree. In- 

 deed, if such living matter is arising, it must be very simple com- 

 pared with protoplasm as we know it to-day; so simple, in fact, 

 that we would not recognize it as such, because the protoplasm 

 of even the simplest organisms has had a long evolutionary history. 



So we may consider it firmly established that, so far as human 

 observation and experiment go, no form of life arises to-day ex- 

 cept from preexisting life by reproduction. The evidence from in- 

 numerable sources converges overwhelmingly to the support of 

 biogenesis. There is no evidence in support of abiogenesis. 



B. Origin of Life on the Earth 



If we accept the testimony of astronomer and geologist, the 

 Earth was at one time in a condition in which life could not f*xist, 



