PERSISTENCE OE PUTREFACTIVE AND INFECTIVE ORGANISMS. 
205 
condition would be readily fulfilled if the liberation of the steam were absolutely 
uniform, and not by fits and starts. But it never is uniform, and if the channel through 
which the steam issues be wide, it is scarcely possible to avoid regurgitation. Some- 
times the pressure within is above that of the atmosphere, and steam freely issues ; but 
at the next moment, through liquid adhesion to the flask and partial condensation 
above, the internal pressure may be below that of the atmosphere and permit air to 
enter. This alternate triumph of the inner and the outer pressure may be rendered 
plainly evident by the motions of the water condensed in the neck of the flask. The 
liquid acts as an index which moves to and fro, sometimes forward, sometimes back- 
ward, as the pressure varies. It is quite evident that contamination may be, and it is 
quite certain that contamination has been, thus introduced into flasks reputed to be free 
from air. 
Even with considerable care and highly disciplined manipulatory skill success is 
not invariable. Ten per cent, is not at all a large allowance to set down as defective 
in ordinary hermetically sealed flasks. The recent opening of about two hundred flasks 
employed in my earlier experiments under water and under caustic-potash solution fur- 
nishes the basis of this conclusion. Even in a comparatively pure atmosphere success 
does not in every instance attend the experimenter. At Kew, for example, on the 8th 
of January, thirteen retort-flasks were charged with infusions of cucumber, melon, beef, 
and sole. Twelve out of the thirteen remained perfectly limpid, but one of them 
(a cucumber-flask) became distinctly cloudy, and this one alone refused, when tested, 
to yield the water-hammer sound. 
§ 30. Experiments with Tumip-clieese infusions. 
I am unwilling to omit all reference to experiments which have cost considerable 
labour, and which, though they have not been repeated and controlled to the extent 
that I could wish, contribute nevertheless to our knowledge of the present question. 
This unwillingness causes me to introduce here, in the briefest manner possible, a 
reference to a series of experiments made with turnip-cheese infusions, so frequently 
cited by Dr. Bastian as offering a conspicuous proof of the doctrine of spontaneous 
generation. 
The experiments to which I refer were made in part with closed chambers and in 
part with hermetically, sealed retort-flasks. The specific gravity of the infusions varied 
from 1008 to 1012. The cheeses employed were Cheshire, Cheddar, Gloucester, Dutch 
cheese, American cheese, Roquefort, and Parmesan, the quantity varying from half a 
grain to two grains for every ounce of the infusion. The cheese being first well tritu- 
rated in a mortar, so as to render its particles very minute, was intimately mixed with 
the infusion, which was then boiled for a few minutes and passed through a filter. 
The filtered liquid was then introduced into its closed chamber, and boiled there for 
five minutes. 
Sixteen such chambers were employed, one of them containing twelve test-tubes, 
each of the others only three. There were therefore fifty-seven test-tubes in all. The 
MDCCCLXXVII. 2 G 
