SPONTANEOUS GBNEHATION. 583 



infection, while 19 out of 20 flasks opened on the Mer de 

 Glace escaped. Our own experiment at the Bel Alp is a 

 more emphatic instance of the same kind, 90 per cent, of 

 the flasks opened in the hayloft being smitten, while not 

 one of those opened on the free mountain ledge was 

 attacked. 



The power of the air as regards putrefactive infection is 

 incessantly changing through natural causes, and we are 

 able to alter it at will. Of a number of flasks opened in 

 1876 in the laboratory of the Royal Institution, 42 per 

 cent, were smitten, while 58 per cent, escaped. In 1877 

 the proportion in the same laboratory was 68 per cent, 

 smitten, to 32 intact. The greater mortality, so to speak, 

 of the infusions in 1877 was due to the presence of hay 

 which diffused its germinal dust in the laboratory air, 

 causing it to approximate as regards infective virulence to 

 the air of the Alpine loft. I would ask my friend to 

 bring his scientific penetration to bear upon all the 

 foregoing facts. They do not prove spontaneous genera- 

 tion to be "impossible." My assertions, however, 

 relate not to " possibilities," but to proofs, and the ex- 

 periments just described do most distinctly prove the 

 evidence on which the heterogenist relies to be written on 

 waste paper. 



My colleague will not, I am persuaded, dispute these 

 results; but he may be disposed to urge that other able 

 and honorable men working at the same subject have 

 arrived at conclusions different from mine. Most freely 

 granted; but let me here recur to the remarks already 

 made in speaking of the experiments of Spallanzani, to 

 the effect that the failure of others to confirm his results 

 by no means upsets their evidence. To fix the ideas, let 

 us suppose that my colleague comes to the laboratory of 

 the Royal Institution, repeats there my experiments, and 

 obtains confirmatory results; and that he then goes to 

 University or King's College where, operating with the 

 same infusions, he obtains contradictory results. Will he 

 be disposed to conclude that the selfsame substance is 

 barren in Albemarle street and fruitful in Gower street or 

 the Strand? His Alpine experience has already made 

 known to him the literally infinite differences existing 

 between different samples of air as regards their capacity 

 for putrefactive infection. And, possessing this knowl- 



