APPENDIX. 329 



failures that, similar to other cases referred to, they finally 

 appeared in the light of accidents. They were, however, 

 by no means uninstructive, for they revealed the existence 

 of breaks in the prevalence of the contaginm, which, under 

 the circumstances, might have been foreseen. 



A rapid glance at the means employed to improve the 

 methods of experiment, and at the results of their employ- 

 ment, may be permitted here. Bulbs, exhausted by an 

 air-pump and afterwards heated almost to redness, were 

 filled when cool with filtered air. While being charged 

 with the infusions the bulbs were warmed, so as to produce 

 a gentle outflow of air, and their necks were sealed while 

 the outflow continued. It was thus sought to avoid the 

 contamination consequent on an indraught. 



The failures resulting from this mode of experiment 

 greatly predominated over the successes. 



Employing similar bulbs, their necks in the first instance 

 were drawn out at the ends to tubes of capillary fineness. 

 The bulbs were then filled each with one-third of an atmo- 

 sphere of filtered air, and, while connected with the air-pump, 

 were heated almost to redness. The capillary tubes were 

 then sealed with the lamp. The sealed ends were afterwards 

 broken ofi" 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 re-seal the capillary tubes without remov- 

 ing them from the liquid. The infusions were afterwards 

 boiled from five to fifteen minutes. 



Here also the fruitfulness of the boiled infusion was 

 the rule, and its barrenness the exception. 



A source of discomfort clung persistently to my mind 

 throughout these severer 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. 



