68 PLANT PHYSIOLOGY 



to the fermented liquor, but these are not due to the yeast, but to the fermentable 

 material in the case of wine, for example, to the grapes. 



215, 1. 36 P. 216, 1. 2,2, for The researches . . . higher plants, read 

 Still BEIJERINCK'S theory does not appear to us to be sound ; the very accurate 

 researches on butyric acid Bacteria argue against it. WINOGRADSKY (1898- 

 1902) has isolated from soil a bacterium of this kind to which has been given 

 the name of Clostridium pasteurianum, and which will occupy our attention 

 later on (Lecture XVIII) on account of its power to assimilate free atmospheric 

 nitrogen. Clostridium agrees morphologically in manypoints with BEIJERINCK'S 

 Granulobacter butyricus, e. g. in the spindle-shaped swellings of the cells and 

 in its granulose reaction previous to the formation of spores. There are other 

 and quite distinct differences between them into which we need not enter here ; 

 the physiological activity of this organism is of more importance for our pur- 

 poses. When supplied with suitable mineral and nitrogenous nutrients it 

 ferments many, but not all, carbohydrates to acetic, butyric, and carbonic acids 

 and hydrogen, about half of the sugar going to the formation of the acids and 

 half to the formation of gases. This whole fermentation process is carried on, 

 according to one of WINOGRADSKY'S experiments, for twenty successive genera- 

 tions, although oxygen was completely excluded. 



Butyric acid-forming organisms have been frequently studied. They 

 differ physiologically from Clostridium (apart from the absence of assimilation 

 of free nitrogen) in their use of numerous fermentable materials (sugar-alcohols, 

 polysaccharides, &c., besides sugar) and by other fermentation products, butyl 

 alcohol being formed as well as butyric acid. Many of these forms are quite 

 as strictly anaerobic as Clostridium, and the relation of two of them to oxygen 

 has been studied in detail by CHUDIAKOW (1878). In the vegetative stage, 

 these species (termed C. butyricum and Bactridium butyricum by CHUDIAKOW) 

 are injured by a brief exposure to ordinary atmospheric air and killed by 

 longer exposure, and even their spores are, in the long run, non-resistant to the 

 action of oxygen. Low concentrations of oxygen can be tolerated, however, 

 without injurious results ; thus Bactridium butyricum grows well in air of 5 mm. 

 pressure, and Clostridium in air of lomm. pressure. 



Again, there are forms, doubtless strictly anaerobic, which indeed are not 

 injured by minute traces of oxygen, but which can thrive without it. Life 

 without free oxygen is indeed possible only if some suitable material which can 

 be fermented is supplied in its place, otherwise such an organism dies under 

 all circumstances, or it requires free oxygen. If fermentation can take the place 

 of respiration it may be concluded that the organism obtains oxygen in the 

 process certainly not free oxygen, but in the combined condition which it 

 separates from its combination. In fact, it may be easily shown that all 

 fermentations are reduction processes. Thus the loosely combined oxygen in 

 oxyhaemoglobin is generally taken up by the fermentative organism, and the 

 oxyhaemoglobin is, as in alcoholic fermentation, reduced to haemoglobin. 

 Reduction of indigo -car mine and methylene blue to the colourless condition 

 is also well known. Fermentable fluids which have such a colouring matter 

 added to them lose their colour if they are excluded from oxygen, but become 

 blue again after being shaken up with air. Further, atmospheric oxygen is 

 absorbed in butyric acid fermentation, if it be presented in non-injurious con- 

 centrations (CHUDIAKOW, 1896). Many organisms which induce fermentation 

 are also capable of splitting off oxygen which is very difficultly accessible ; 

 thus nitrates and sulphates in nature are so reduced. Both of these processes 

 must be considered in detail because they are of importance in the circulation 

 of life on the earth. 



Reduction of sulphates occurs in nature especially in the mud of fresh 



