202 
PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
atmospheres of oxygen were employed. In all cases, however long the pressure was 
continued, or however favourable to putrefaction the surrounding temperature might 
be, the infusions (which embraced those of beef, mutton, and turnip) were found, when 
taken from the bottles, as clear as crystal and entirely free from life. It required, 
indeed, long subsequent exposure to the common air to infect infusions which had 
been thus surcharged with oxygen. Other bottles containing the same infusions were 
simultaneously subjected to a like pressure, not of oxygen, however, but of atmospheric 
air. When removed from the bottles they were one and all found in a state of putre- 
faction and swarming with life. 
Thus when oxygen is wholly withdrawn from organic infusions, the life with which 
we are here concerned ceases. When, on the other hand, the gas is in considerable 
excess, it becomes a deadly poison to organisms which, in moderate quantities, it sustains. 
As in the case of temperature, so in regard to the supply of oxygen, there is a median 
zone favourable to the play of vitality, beyond which, on both sides, life cannot exist. 
The present memoir virtually ends here ; but I will append a few brief sections 
which, though incomplete, are not without instruction. 
§ 27. Experiments on neutralized TJrine. 
I have already communicated to the Royal Society the result of some experiments 
made with this liquid*, in which the potash employed for neutralization was subjected 
to a temperature of 220° Fahr. The alkali was contained in tubes drawn out finely at 
the end, which were introduced into the flasks containing the urine, and broken by 
shaking after the acid urine had been completely sterilized by heat. The . cases were 
exceedingly rare in which life showed itself in the urine thus neutralized. The prepon- 
derance of sterilized flasks over unsterilized ones was enormous. 
In the experiments now to be glanced at, neither the urine nor the potash was raised 
to a temperature higher than 212°. Wishing to ascertain how the refractory germs of 
our laboratory would fare in neutralized urine, on the 16th of February I had five pipette- 
bulbs charged with the liquid. It was neutralized by caustic potash, which on boiling 
produced copious precipitation. It was afterwards filtered and rendered very transparent. 
The bulbs had been well cleansed, filled with one third of an atmosphere of filtered air, 
hermetically sealed, and exposed afterwards to the heat of a Bunsen flame. They were 
charged with the urine by breaking off their finely drawn out points in the body of the 
liquid. They were then again sealed, and subjected to the boiling temperature for ten 
minutes. 
Not one of these bulbs remained sterile. Two days subsequent to their preparation 
they were all swarming with organisms. 
Three other bulbs were on the same occasion charged with precisely the same infusion, 
only instead of being associated with air they were well purged of air by five minutes’ 
boiling in an oil-bath. While the steam was issuing they were hermetically sealed. 
* Proceedings, vol. xxv. p. 457. 
