74 PRESERVATION OF FOOD BY REFRIGERATION ; 
mucors and mucidines, which possess the remarkable property of 
exciting the oxidation of a great number of organic principles, 
such as sugars, alcohols, organic acids, albumenoids, nitrogenous 
matter, etc., at the expense of the oxygen of the air. 
“After having proved by careful experiments that spontaneous 
slow combustion of animal or vegetable substances depends 
necessarily on the development of organisms in the interior or on 
the surfaces of the substances which are in process of decomposi- 
tion, and that without organisms there is neither combustion nor 
absorption of oxygen, M. Pasteur traces the following picture of 
putrid decomposition in contact with air :— 
“*Kven the most easily decomposed animal matter, as, for 
instance, blood or urine, may be preserved for an indefinite length 
of time in air which has been calcined or deprived of its germs ; 
under these conditions the absorption of oxygen is but trifling and 
putrefaction does not take place, and at the same time no infusoria 
are produced. 
“Tf, on the contrary, this same substance remains exposed to 
the ordinary air, it is oxidised, putrefies, and infusoria are 
developed. It is commonly known that putrefaction takes a 
certain time to declare itself—a period varying according to the 
circumstances of temperature, of the neutral, acid, or alkaline 
character of the liquid. Under favourable circumstances, twenty- 
four hours are required before the phenomenon begins to manifest 
itself by external signs. During the first period, an internal 
movement takes place in the liquid, the effect of which is to 
withdraw entirely the oxygen of the air which is in solution, 
and to substitute for it carbondioxide gas. The total disappearance 
of the oxygen, when the medium is neutral or slightly alkaline, is 
generally due to the development of the smallest kinds of 
infusoria, especially the A/onas crepusculum and the Bactertum 
termo. A very slight troubling then takes place, because these 
little beings pass about in all directions. If the vessel containing 
the putrescible liquid has a large opening to the air, the bacteria 
perish only in the liquid mass, after the removal of the oxygen, 
while they continue, on the contrary, to propagate ad ‘afinitum on 
the surface, because it is in contact with the air. There they cause 
a thin film to form, which goes on thickening by degrees until it 
falls to the bottom of the vessel, then another forms, and so on 
continually. This film, to which different mucors and mucidines 
are attached, prevents the solution of oxygen gas in the liquid, 
and consequently allows the development of vibrios. With respect 
to these latter organisms, the vessel is as if it were closed against 
the introduction of air. 
