FERMENT A TION 2 15 



oxygen by pumping it out and by passing hydrogen through it, the remainder 

 he got rid of by adding an easily oxidizable body (sodium hydrosulphide). When 

 free oxygen is completely absent unlimited growth of the bacterium takes place 

 and, at the same time, very active fermentation. But whenever the least traces 

 of oxygen are present the organism begins to assume a somewhat different 

 appearance from the strictly anaerobic form and forms no spores. Beijerinck 

 (1894 and 1899) denies that we have here to deal with a vital process which goes 

 on entirely without oxygen and without normal respiration, although he succeeded 

 in carrying out seven cultures one after the other without oxygen being present, 

 and although he found an increase from one to many millions taking place — 

 not as in the case of yeast from one to twenty- or thirtyfold only. What led 

 him to this conclusion was specially the behaviour of the bacterium under a 

 cover-glass. Many motile Bacteria strive to reach the concentrations of oxygen 

 which suit them best, and collect in such regions ; if they be placed on a 

 slide and covered by a cover-glass only a very limited quantity of oxygen 

 can reach them, for the amount of oxygen dissolved rapidly decreases from 

 the edge of the cover-glass inwards. Genuine aerobes collect at the edge of the 

 preparation, genuine anaerobes, on the other hand, in the centre ; Bacillus 

 hutylicus places itself at a certain distance from the periphery, where a low but 

 not a minimum pressure of oxygen exists. The organism thrives also on other 

 nutritive substrata, e. g. i per cent, solution of peptone with \ per cent, of 

 starch paste, but induces fermentation only when air can enter easily ; only 

 in sweetwort can it form many generations one after the other without free 

 oxygen. Hence Beijerinck held that the sweetwort contained an oxygen 

 reserve combined in some way and yet accessible to the bacillus, and believed 

 that all Bacteria, even the so-called obligate anaerobes use small quantities 

 of oxygen, and thus that there are no organisms which are able to do without 

 free oxygen. Even if Beijerinck be right in his conclusions the distinc- 

 tion between aerobes and anaerobes, or as Beijerinck puts it, between 

 aerophiles and micro-aerophiles is still perfectly well marked, for the consump- 

 tion of oxygen in the latter is still far from being sufficient to render possible a 

 respiration capable of maintaining the necessary supply of energy ; fermenta- 

 tion must always assist in the process. It is possible that certain functions are 

 carried out only when respiration takes place, while other functions may be 

 performed at the expense of the energy supplied by fermentation. 



The researches of Chudiakow (1896) form a useful supplement to those 

 of Beijerinck, and they ought to be mentioned here, although they do not 

 deal with Bacillus hutylicus, but with two butyric acid-producing Bacteria 

 termed Clostridium hutyricum and Bactridium hutyricum. Both these forms are 

 strongly anaerobic ; in their vegetative condition they are injured by a brief 

 exposure to ordinary air and are killed by longer exposure ; even their spores 

 cannot in the long run resist the action of oxygen, although small quantities of 

 oxygen do not produce any injury. Bactridium hutyricum can develop quite well 

 in air with a pressure of 5 mm., and Clostridium at a pressure of 10 mm., and, 

 what is most noteworthy, the small quantities of oxygen present in the culture 

 are, under these conditions, completely absorbed and utilized by the organism. 



Chudiakow' s experiments do not lead us to the conclusion that the develop- 

 ment of the butyric acid Bacteria mentioned depends on the presence of combined 

 oxygen in a medium that possesses no free oxygen, in the same way as Beijerinck 

 asserted for Bacillus hutylicus, for they grow on dextrose or saccharose, maltose, 

 starch, lactose, and mannite, in combination with peptone or asparagin, urea, 

 ammonium chloride (but not with nitrates), exactly like anaerobes. Since 

 again, the presence of combined oxygen in wort is (in Beijerinck's researches) 

 problematical, the last word has not as yet been spoken as to the nature of 

 anaerobiosis ; yet it is extremely probable that the organisms concerned can 

 live without oxygen. On the other hand, there is always the possibility that 



