330 APPENDIX. 



A plan was therefore resorted to, by which the infusions 

 were driven by atmospheric pressure through lateral chan- 

 nels issuing from the centres of the bulbs. As before, each 

 bulb was filled with one-third of an atmosphere of filtered 

 air, and afterwards heated nearly to redness. When fully 

 charged, the infusion rose higher than the central orifice, 

 and no portion of the internal surface was wetted save that 

 against which the liquid permanently rested. The lateral 

 channel was then closed with a lamp without an instant's 

 contact being permitted to occur between any part of the 

 infusion and the external air. It was thus rendered ab- 

 solutely certain that the contagia exposed subsequently to 

 the action of heat were to be sought, neither in the super- 

 jacent air nor on the interior surfaces of the flasks, but in 

 the body of the infusions themselves. 



By this method I tested in the first place the substance 

 which, at an early stage of the inquiry, had excited my 

 suspicion — without reference to which the discrepancy 

 between the behaviour of infusions examined in the winter 

 of 1875-76 and those examined in the winter of 1876-77 is 

 inexplicable, but by reference to which the explanation of 

 the observed discrepancy is complete ; I mean, the old hay 

 which cumbered our laboratory floor. 



Four hours' continuous boiling failed to sterilize bulbs 

 charged with infusions of this hay. In special cases, more- 

 over, germs were found so indurated and resistant that 

 five, six, and, in one case, even eight hours' boiling failed to 

 deprive them of life. 



All the difficulties encountered in this long and laborious 

 inquiry were traced to the germs which exhibited the ex- 

 traordinary powers of resistance here described. They 

 introduced a plague into our atmosphere — the other in- 

 fusions, those of fresh hay included, like a smitten popula- 

 tion, becoming the victims of a contagium foreign to 

 themselves.^ 



It is a question of obvious interest to the scientific 



* A hard and wiry hay from Guildford, which I have no reason 

 to consider old, was found extremely difficult to sterilize. 



