614 



VITAL ACTIONS OF THE LOWER FUNGI. 



Influence of 

 course 1 oftb 



Pasteur' 



play an active part in it usually hinder the development 

 of other forms. All these accompanying micro-organisms 

 must complicate the putrefactive process, in that the 

 specific products of their tissue change become mixed 

 with the products of the fermentation. 



Oxygen exerts the greatest influence on the course of 

 the putrefactive process, [t has been long known that 

 true P utre f acti on, with foul-smelling gaseous products, 

 occurs only when the amount of air is limited. When 

 air is freely admitted these odours are absent, and a 

 rapid and very complete oxidation of the putrescible 

 materials takes place, thip form of putrefaction being 

 therefore designated under the special name decay. 

 Pasteur was the first to indicate more clearly the differ- 

 ence between putrefaction in the presence of oxygen, and 

 putrefaction without oxygen; according to Pasteur, when 

 air is excluded, the oxygen contained in the fluid is, in 

 the first place, used up completely by certain micro- 

 organisms (monas crepusculum and bacterium termo). 

 As soon as the oxygen is removed these bacteria die, and 

 fall to the bottom of the vessel in the form of a deposit. 

 The true After this has occurred the true putrefactive bacteria 



putrefactive . . , 



organisms are appear; they can only exist where oxygen is absent; 



anaerobes. ^ey ge j. U p ^ putrefactive fermentation, and absolutely 

 require the preparatory action of these aerobes. If, on 

 the other hand, the fluid is freely exposed to air, the 

 aerobic bacteria develop continuously at the surface and 

 form a scum, which at times falls to the bottom in 

 masses, but is constantly regenerated. This scum pre- 

 vents the access of the oxygen to the fluid, and thus it 

 is possible that vibriones, which can only live when 

 oxygen is absent, but which cause the fermentations, can 

 -develop in the fluid, as it were under the protection of 

 the bacterial cover. The somewhat complex fermentative 

 products thus formed serve as nutriment to the aerobes 

 at the surface, and the latter then break them up into 

 the simplest compounds, water, carbonic acid, ammonia, 

 and thus the products which are ordinarily characteristic 

 of putrefaction are not found. 



In this way Pasteur sought to explain the difference 



