PUTREFACTION. G15 



between putrefaction in the presence and in the absence Putrefaction 



f . i , i i , i e f also occurs in 



of oxygen, in correspondence with his theory of fer- the presence 

 mentation based on the absence of this gas. This view of ox y en - 

 is, however, evidently not quite correct. As the result 

 of more recent investigations, it has been shown 

 'beyond doubt that, as well in the presence as in the 

 absence of oxygen, certain kinds of bacteria are able 

 to split up the albuminoid molecule and furnish the 

 products characteristic of putrefaction. Further also, 

 we have in the chemical processes which occur in putre- 

 faction a partial explanation of the influence of oxygen. 



When oxygen is absent extensive reduction processes 

 occur, which, for the most part, arise directly in the pro- 

 cess of fermentation ; fatty acids are formed from oxy- 

 acids; marsh gas, sulphuretted hydrogen, sulphur (for 

 example in the beggiatoa) appear ; above all, however, 

 hydrogen is formed in the various fermentations. As is 

 evident from the formulae given above, hydrogen is processes 

 liberated in the fermentation of formic acid, lactic acid oxyg-en'i? a 

 (butyric acid fermentation), glycerinic acid, malic acid, present - 

 tartaric acid, erythrite, leucin, &c. ; this hydrogen must 

 at times lead to further reduction effects. Nitrates must 

 be converted by this hydrogen into nitrites, indigo blue 

 into indigo white, invert sugar into mannite ; sulphates 

 can also probably be reduced by it. On the whole, how- 

 ever, the alteration of the fermentescible material and of 

 the products of fermentation, as the result of the action of 

 the hydrogen, is only slight, and it is characteristic of the 

 course of fermentation without oxygen that the true fer- 

 mentative products appear in the main in an unaltered 

 condition without having undergone further destruction 

 and oxidation ; and also we can understand that in this 

 process of putrefaction only those bacteria can exist 

 which are able to act without the presence of oxygen, so 

 long as they have fermentescible material at their 

 disposal. 



The case is otherwise when there is free access of Role of the 

 oxygen. In this case the same hydrogen which in the hydrogen. 

 former instance only performed a secondary function, 

 probably now plays a much more important part. 



