Pasteur's Researches on Putrefaction. 101 



have paid attention to infusoria. I reserve, so far as it con- 

 cerns me, the question of the identity or the difference of these 

 species, and of the variety of their forms, subordinated to 

 changes in the condition of the medium in which they live. I 

 accept them provisionally such as they are described, and I 

 arrive at the conclusion that these six species of vibrions are six 

 species of animal ferments, and that they are the ferments of 

 putrefaction. Besides this, I have shown that all these vibrions 

 can exist without free oxygen, and that they perish in contact 

 with this gas, if nothing preserves them from its direct action. 

 The fact that I announced to the Academy two years ago, and 

 of which I have recently pointed out a second example, namely, 

 that there exist animalcule ferments of the genus Vibrio which 

 can live without free oxygen, was only a particular incident 

 appertaining to a mode of fermentation which is perhaps the 

 most wide-spread in nature. 



" The conditions under which putrefaction is manifested may 

 vary considerably. Suppose, in the first instance, the case of a 

 liquid, that is to say of a putrescible substance, of which all the 

 parts have been exposed to contact with the air. Either this 

 liquid may be shut up in a close vessel, or it may be placed in 

 an open vessel, having an aperture more or less large. I will 

 examine in succession what happens in the two cases. 



" It is commonly known that putrefaction takes a certain 

 time to manifest itself, and that this time varies according to 

 temperature, neutrality, acidity, or alkalinity of the liquid. 

 Under the most favourable circumstances a minimum of about 

 twenty-four hours is necessary before the phenomenon begins 

 to be manifested by external signs. During this first period 

 the liquid is agitated by an internal movement, the effect of 

 which is to deprive of its oxygen the air which is in solution, 

 and to replace it by carbonic acid gas. The total disappearance 

 of the oxygen when the liquid is neutral or slightly alkaline is 

 due, in general, to the development of the smallest of the in- 

 fusoria, the Monas crepusculum and Bacterium termo. A very 

 slight agitation occurs as these little beings travel in all direc- 

 tions. When this first action of exhausting the oxygen in 

 solution is accomplished, they perish and fall to the bottom of 

 the vessel like a precipitate ; and if by chance the liquid con- 

 tains no fecund germs of the ferments I have spoken of, 

 it remains indefinitely in this condition without putrefaction — 

 without fermenting in any way. This is rare, but I have met 

 with several examples. Most frequently when the oxygen in 

 solution has disappeared, the vibrion ferments, which have no 

 need of this gas, begin to appear, and putrefaction immediately 

 sets in. Gradually it accelerates itself, following the progres- 

 sive march of the development of the vibrions. The putridity 



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