THE BEGINNINGS OF II FE. id^ 



are bound, in such an enquiry, to act on the suppo- 

 sition that germs may be universally distributed through 

 the air, water, and all other substances employed. 

 Accepting such possibilities, and acting as carefully as 

 if they had been established truths, we have neverthe- 

 less been able to show that living matter does make 

 its appearance within sealed vessels in which, as we 

 are fully entitled to believe, all pre-existing living 

 matter had been destroyed. 



Further, we have pointed out that the microscope 

 alone may teach us how little all that has been pre- 

 viously written concerning the universal distribution 

 of germs has any direct bearing upon the question of 

 the mode of origin of the primordial forms of life^. 

 It is useless to look in the air for invisible germs; 

 and yet the careful microscopical examination of films 

 of fluid 2 teaches us that if Bacteria arise from pre- 

 existing germs at all, these germs must have pre-existed 

 in an invisible state -3. 



In the present stage of our enquiries, however, — now 

 that we are engaged in tracing the organic forms suc- 

 cessively assumed by new-born living matter and its 

 derivatives in infusions, or other fluids, exposed to the 

 air — it becomes desirable that we should, know what 



^ See vol. i. p. 297 ; and ' Nature,' 1870, No. 47, p. 410, 



^ See vol. i. p. 295. 



3 It has been shown, not only that Bacteria, Toridce, and other forms 

 can arise de novo, but also that the air does not contain any appreciable 

 number oi Bacteria germs, whether visible or invisible. (See pp. 5-7.) 



