250 LIFE AND DEATH. 



mentary animal. This would indeed be an irrefutable 

 proof that the germs of all vital activity are contained 

 in the molecular activity of brute bodies, and that 

 there is nothing essential to the latter that is not 

 found in the former. 



Unhappily this demonstration cannot be given. 

 Science furnishes no example of it, and we are forced 

 to have recourse to the slow method. 



The question here involved is that of spontaneous 

 generation. It is well known that the ancients 

 believed in spontaneous generation, even for animals 

 high in the scale of organization. According to 

 Van Helmont, mice could be born by some incom- 

 prehensible fermentation in dirty linen mixed with 

 wheat. Diodorus speaks of animal forms which were 

 seen to emerge, partly developed, from the mud of 

 the Nile. Aristotle believed in the spontaneous birth 

 of certain fishes. This belief, though rejected as to 

 the higher forms, was for a long time held with 

 regard to the lower forms of animals, and to insects — 

 such as the bees which the shepherd of Virgil saw 

 coming out from the flanks of the dead bullock — 

 flies engendered in putrefying meat, fruit worms and 

 intestinal worms ; finally, with regard to infusoria 

 and the most rudimentary vegetables. The hypo- 

 thesis of the spontaneous generation of the living 

 being at the expense of the materials of the ambient 

 medium has been successively driven from one 

 classificatory group to another. The history of the 

 sciences of observation is also a history of the con- 

 futation of this theory. Pasteur gave it the finishing 

 stroke, when he showed that the simplest micro- 

 organisms obeyed the general law which declares 

 that the living being is formed only hy filiation — that 



