THE ORIGIN OF LIFE 95 



thesis the simplest albuminoid ; even the chemical structure of 

 the organic substance still remains an impenetrable mystery, and 

 yet some one will attempt to make a living plant or animal. 



These experiments by Pouchet, which sometimes really 

 appeared to be crowned with success, were soon proved to have 

 been abortive. Subsequent experiments showed beyond doubt 

 that the fungi, bacteria, &c., which sometimes did appear in the 

 cultures had developed from germs which had entered the test 

 tubes from without. As long ago as 1838 Ehrenberg demon- 

 strated that the entire atmosphere is filled with desiccated animal 

 and plant germs, that these are carried by wind and weather over 

 vast distances until by chance they fall upon favourable soil and 

 there re-awaken to new life. Moreover, Ehrenberg had rendered 

 it highly probable that in all those cases in which infusoria 

 or fungi are observed it is not a generation out of nothing or 

 out of inorganic matter which we are observing, but merely a 

 development out of already existing germs. 



But an opinion once formed is not easily eradicated. As 

 Schopenhauer aptly observed, " A hypothesis leads in the mind 

 in which it has settled, or was perhaps created, a life which 

 resembles that of an organism, in so far as it absorbs from the 

 outer world only that which is homogeneous and digestible and 

 rejects the heterogeneous and injurious, or excretes it in toto if 

 it was unavoidably introduced." In the same manner the idea 

 of generation without ancestors, and even of an artificial genera- 

 tion of unicellular organisms, reappears from time to time in a 

 few fantastic minds. 



Later investigators at first Theodor Schwann, afterwards 

 Ferdinand Schultze, Pasteur and others proved definitely that 

 neither bacteria, nor fungi, nor any protozoa could be generated 

 in vessels with infusions of meat or hay in which at first all 

 germs of life had been carefully killed by exposing them for 

 some time to a boiling temperature and then enclosing them in 

 air-tight tubes. (This is the well-known process adopted in the 

 preservation of various foodstuffs which retain their wholesome- 

 ness for a very considerable time if sterilization has been 

 sufficiently thorough.) But if afterwards the tubes which had 

 thus been rendered free from germs were opened and thus 

 enabled freely to admit ordinary air it did not, as a rule, take 



