9 8 



BIOGENESIS AND HOMOGENESIS 



smallest solid particles by having to pass through the close 

 meshes of the cotton-wool. 



Experiments of this sort conducted with proper care have 

 been known for many years to give negative results in the 

 great majority of cases : the fluids remain perfectly sterile 

 for any length of time. But in certain instances, in spite of 

 the most careful precautions, bacteria were found to appear 



FIG. 20. A Beaker with a number of test-tubes containing putres- 

 cible infusions and plugged with cotton-wool. (From Klein.) 



in such fluids, and for years a fierce controversy raged 

 between the biogenists and the abiogenists, the latter in- 

 sisting that the experiments in question proved the occurrence 

 of spontaneous generation, while the biogenists considered 

 that all such cases were due to defective methods either to 

 imperfect sterilization of the fluid or to imperfect exclusion 

 of germ-containing atmospheric dust. 



The matter was finally set at rest, and the biogenists 



