234 



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



with one third of an atmosphere of filtered air, and, while connected with 

 the air-pump, were heated almost to redness. The capillary tubes were 

 then sealed with the kmp ; the sealed ends were afterwards broken off 

 in the body of the liquid, two thirds of each bulb being thus filled with the 

 infusion. By great care it was found possible to reseal the capillary 

 tubes without removing them from the liquid. The infusions were after- 

 wards boiled from five to fifteen minutes. 



Here also the fruitfulness of the boiled infusion was the rule, and 

 its barrenness the exception. 



One source of discomfort clung persistently to my mind through- 

 out these experiments. I was by no means certain that the observed 

 development of life was not due to germs entangled in the film of 

 liquid adherent to the necks and higher interior surfaces of the 

 bulbs. This film might have evaporated, and its germs, surrounded by 

 air and vapour, instead of by water, might on this account have been 

 able to withstand an ordeal to which they would have succumbed if 

 submerged. 



A plan was therefore resorted to by which the infusions were driven 

 by atmospheric pressure through lateral channels issuing from the centres 

 of the bulbs. As before, each bulb was filled with one third of an atmo- 

 sphere 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 

 absolutely certain that the contagia exposed subsequently to the action 

 of heat were to be sought, neither in the superjacent air nor on the in- 

 terior surfaces of the flasks, but in the body of the infusions them- 

 selves. 



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 dis- 

 crepancy is complete ; I mean, the old hay which cumbered our laboratory 

 floor. 



Tour hours' continuous boiling failed to sterilize bulbs charged with 

 infusions of this hay. In special cases, moreover, 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 extraordinary powers 

 of resistance here described. They introduced a plague into our 



