334 FRAGMENTS OF SCIENCE 



mit 10 per cent of our flasks to take in air without con- 

 tracting contamination. A quarter of a century ago Pasteur 

 proved the cause of "so-called spontaneous generation" to 

 be discontinuous. I have already referred to his observa- 

 tion that 12 out of 20 flasks opened on the plains escaped 

 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 Eoyal 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 generation to be 

 "impossible." My assertions, however, relate not to "pos- 

 sibilities," but to proofs, and the experiments just de- 

 scribed 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 



