SPONTANEOUS GENERATION. 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 Koyal 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 Koyal Institution, repeats there my experiments, and 
obtains confirmatory results; arid 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- 
