230 



Prof. J. Tyndall on the Deportment of [May 17, 



I need not remark on the imperviousness of cheese to water, and its con- 

 sequent power to prevent diffusion. 



These summer experiments on turnip-cheese infusions were, however, 

 merely tentative, and I purpose completing them hereafter. 



In the autumn I resumed experiments on infusions of hay, which had 

 been purposely postponed. With this substance no difficulty was encoun- 

 tered in my first inquiry. Boiled for five minutes, and exposed to air 

 purified spontaneously, 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 transparency, I have, in a great number of cases, inocu- 

 lated this infusion with the smallest specks of animal and vegetable 

 liquids containing Bacteria, and observed, twenty-four hours afterwards, 

 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 experi- 

 mented so easily and successfully a year previously appeared to have 

 changed its nature. The infusions extracted from it bore, in some cases, 

 not only five minutes' but fifteen minutes' boiling with impunity. On 

 changing the hay a different result was often obtained. Many of the 

 infusions extracted from samples of hay purchased in the autumn of 1876 

 behaved exactly like those extracted from the hay of 1875, being com- 

 pletely sterilized by five minutes' boiling. 



The possible influence of age and dryness soon suggested 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 sub- 

 jected to long-continued desiccation. 



As the inquiry proceeded the distinction between old and new hay 

 became more and more blurred, while prolonged experiment with hay of 

 various kinds failed to rescue the question from uncertainty. I there- 

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

 melon, beetroot, and artichoke, for example, whose parasitic or epiphytic 

 -germs were unlikely to have suffered desiccation. 



Boiled for periods varying from five to fifteen minutes and exposed 

 afterwards to moteless air, in numberless experiments these infusions 

 broke down, charging themselves throughout with organisms, and loading 

 themselves, almost in all cases, with a soapy corrugated scum. 



I then fell back upon infusions whose deportment had been previously 

 familiar to me, and in the sterilization of which I had never experienced 

 any difficulty. Eish, flesh, and vegetables were resubjected to trial. 



