200 
PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
large number of retort-flasks, embracing infusions of snipe, wild duck, partridge, hare, 
rabbit, mutton, turbot, salmon, whiting, mullet, turnip, and hay, had remained over 
from my stock of 1875. After a year’s exposure to the temperature of our warm room 
not one of these flasks showed the slightest trace of turbidity or life. On the 7th of 
December the sealed ends of forty of them were snipped off in the laboratory. Five days 
afterwards twenty-seven of them were found swarming with organisms — a considerably 
higher percentage than that obtained by the same process in the same laboratory a year 
previously. 
It is needless to dwell with any emphasis on the obvious inference from all this, 
namely, that the contagium is external to the infusions (that it is, something in the air), 
and that at different times w.e have different amounts of aerial interspace free from the 
floating contagium. 
§ 25. Critical Review of the last two Sections. 
It has been my desire and aim throughout this inquiry to free it as much as possible 
from uncertainty and doubt. I have tried to render the facts safe by laborious repetition, 
and to render the interpretations of those facts secure by close and constant criticism. 
Thus, in reference to our present subject, I had to put to myself very definitely the 
question whether the permanent clearness of an infusion exposed to a very moderate 
amount of heat, after having been freed from air by boiling or by the Sprengel pump, 
was really due to the destruction of the germs in the infusion. Even in a highly infec- 
tive atmosphere from three to five minutes’ boiling in an oil-bath suffices to sterilize our 
retort-flasks, while it is perfectly certain that exposure to the boiling temperature for 
fifty times this interval fails to kill the germs of an infusion containing a good supply 
of atmospheric air. A similar remark applies to our experiments with the Sprengel pump. 
I asked myself whether in these cases the life of the germs was not suspended merely, 
instead of being destroyed. It was quite conceivable that germs endowed with vital 
power, ready to act under proper conditions, might still exist in our hermetically sealed 
flasks, although the entire absence of oxygen rendered their further development 
impossible. 
That something more than a mere temporary hindrance to development is here 
involved was, however, proved by many of the experiments just recorded. These expe- 
riments showed that after hermetically sealed flasks had remained pellucid, not only for 
days but for weeks and months, and in some cases for more than a year, when their 
sealed ends were broken off, even in ordinary air, they by no means invariably showed 
signs of life afterwards. Many of them remained permanently barren while copiously 
supplied with oxygen. 
Special experiments were, however, made to illustrate this point. First of all, as I 
have already recounted, hermetically sealed retort-flasks were opened in one of our lower 
store-rooms, and though supplied with oxygen from this source they showed subsequently 
no signs of life. A considerable number of retort-flasks had also their sealed ends 
