324 APPENDIX. 



In the aTitumn I resumed experiments on infusions o£ 

 hay, which had been purposely postponed. With this sub- 

 stance no diflficulty was encountered in my first inquiry. 

 Boiled for five minutes, and exposed to air purified spon- 

 taneously, or freed from its floating matter by calcination 

 or filtration, hay-infusion, though employed in multiplied 

 experiments at various times, never showed the least 

 competence to kindle into life. After months of trans- 

 parency, in a great number of cases, I inoculated this 

 infusion with specks of animal and vegetable liquids con- 

 taining Bacteria, and observed, twenty-four hours after- 

 wards, its colour lightened and its mass rendered opaque 

 by the multiplication of these organisms. 



But in the autumn of 1876, the substance with which 

 I had experimented so easily and successfully a year pre- 

 viously appeared to have changed its nature. The in- 

 fusions extracted from it bore, in some cases, not only five 

 minutes' but fifteen minutes' boiling with impunity. On 

 changing the hay a different r'^sult was often obtained. 

 Many of the infusions extracted from samples of hay pui'- 

 chased in the autumn of 1876 behaved exactly like those 

 extracted from the hay of 1875, being completely sterilized 

 by five minutes' boiling. 



The possible influence of age and dryness soon sug- 

 gested itself, and I tested the surmise to the uttermost. 

 Numerous and laborious experiments were executed with 

 hay derived from different localities ; and by this means, 

 in the earlier days of the inquiry, it was revealed that the 

 infusions which manifested this previously unobserved 

 resistance to sterilization were, one and all, extracted from 

 old hay, while the readily sterilized infusions were 

 extracted from new hay, the germs adhering to which had 

 not been subjected to long-continued desiccation. 



As the inquiry proceeded the distinction between old 

 and new hay became more and more blurred, while pro- 

 longed experiment with hay of various kinds failed to 

 rescue the question from uncertainty. I therefore turned 

 to substances of a succulent nature — to fungi, cucumber, 



