224 SOME PRIMITIVE BELIEFS 



been formerly ascribed to a mysterious power of breeding 

 these organisms possessed by inanimate dirt and refuse. 



In spite of this progress in knowledge the belief in 

 " spontaneous generation " of such excessively minute 

 organisms as the bacteria and yeasts was general until 

 Theodore Schwann in 1836 performed with them just the 

 same experiment as Redi had performed with blow-flies 

 in 1668. He showed that if a putrescible liquid (for 

 instance, soup) were boiled in a retort so as to destroy all 

 germs, and then the open neck of the retort was kept heated 

 in a flame, so that no floating germs could enter alive, the 

 soup did not putrefy, and no bacteria or other organisms 

 appeared in it. The old notions, nevertheless, survive to 

 this day. Peasants, fisher-folk, and even uneducated 

 wealthy countrymen cling to them with the confidence 

 arising from profound ignorance. And occasionally a 

 man of some scientific training and knowledge astonishes 

 the world by a futile attempt to show that the old fancies 

 were true in regard, at any rate, to the lowest microscopic 

 forms of life. But these are but the echoes of the past ; 

 we do not believe nowadays in " spontaneous genera- 

 tion," nor in sudden transformations of lower into higher 

 forms of life. The doctrine, " omme vivum e vivo " every 

 living thing (in the present condition of our earth) is born 

 from a living thing is now held by scientific investigators 

 as a reasonable generalisation of experience. 



On the other hand, Harvey's dictum, " Every living 

 thing comes from an egg," is only true in a limited sense, 

 namely, that whilst the individual among most larger 

 animals and plants is always traceable to an egg-cell 

 detached from a parental individual of a like kind or 

 species, there are whole groups and series of lower animals 

 and most plants in which the individual born or 

 " developed " from an egg-cell does not proceed when 

 grown to full size to reproduce in turn by eggs and fer- 



