58 
PROFESSOR TYNDALL ON THE OPTICAL DEPORTMENT OE THE 
§ 24. Developmental Power of Infusions and Solutions: Air-germs contrasted with 
Water-germs. 
Wishing to make no experiment, whether with self-cleansed, filtered, or calcined air, 
or with infusions withdrawn from air by the air-pump, or contained in hermetically 
sealed vessels, without exposing the same infusions to ordinary air, this comparison was 
instituted on the present occasion. One hundred test-tubes, an inch wide and 3 inches 
deep, were divided into groups, each being filled with the same infusion. The groups were 
sufficiently numerous to embrace all the substances mentioned in the last Table. Exposed 
to the uncleansed air, they were attacked with different degrees of rapidity and vigour ; 
but in a few days all of them without exception became muddy and crowded with life. 
On the whole, the hare- and pheasant-infusions presented the greatest contrast. The 
tubes containing the former were far gone before those containing the latter were 
sensibly invaded. The putrescibility of the pheasant, moreover, was exceeded by that 
of the snipe, partridge, and plover. The sheep’s heart examined was also slow to 
putrefy. A single illustration of this difference of developmental power may be given 
here. 
On the 13th of November thirty tubes, containing infusions of partridge, pheasant, 
snipe, hare, sheep’s heart, and codfish, five tubes being devoted to each, together with 
four tubes of plover, three of mullet, and three of liver, were exposed to the laboratory 
air. On the 15th, 16th, and 22nd the numbers taken possession of by Bacteria were 
as follows : — 
Partridge 
Pheasant 
Snipe . 
Hare . 
Heart 
Codfish 
Plover 
Mullet 
Liver . . 
15th. 
0 
0 
2 
2 
0 
2 
1 
1 
1 
16th. 
3 
1 
3 
4 
1 
4 
2 
2 
3 
22nd. 
all 
99 
99 
99 
97 
99 
99 
99 
They had probably all given way some days before the 22nd, but I had not taken the 
precaution to look at them. 
Thus, then, the first two days produced no visible change in the pheasant-infusion, 
while in two of the hare-tubes putrefaction had vigorously set in. Three days’ exposure 
caused only one of the pheasant-tubes to yield ; four of the hare-infusion had yielded in 
the same time. The difference between them was also illustrated by the mould upon 
their surfaces. Some days after their exposure four of the five pheasant-tubes were 
thickly covered with Penicillium , while the five hare-tubes, with one exception, which 
could hardly be considered such, had repelled the enemy, maintaining their Bacteria 
undisturbed. 
