202 ANAEROBIOSIS 



as a depolarizer to unite with the nascent hydrogen formed from the water, and upon this 

 basis Mathews has formulated the following hypothesis: "Certain active particles in the 

 protoplasm attack the water which is decomposed into oxygen and hydrogen. The oxygen 

 combines with substances of the protoplasm thus oxidizing them; the hydrogen is either set 

 free in gaseous form or it is united with atmospheric oxygen to form water, or it combines 

 with other substances in the protoplasm."' In the words of Packard:^ "Respiration is the 

 dissociation of water with the liberation of hydrogen and the real respiration is brought 

 about not by the oxygen of the air but by that of the water. If atmospheric oxygen is present 

 it unites with the hydrogen set free from the water, thus acting as a depolarizer. According 

 to this theory, aerobic and anaerobic respiration are identical; the only difference is that the 

 anaerobic protoplasm is a powerful enough reducing agent to drive the hydrogen out of the 

 water and let it escape as free hydrogen." Mathews' suggested that other oxidizing sub- 

 stances may replace atmospheric oxygen as a depolarizer and stimulate oxidation in the 

 absence of air. This may, indeed, be the role of carbohydrates and of other organic substances 

 in anaerobiosis. Theobald Smiths showed that some facultative anaerobes behave as obligate 

 aerobes in sugar-free broth, growing only in the open arm of the fermentation tube, while 

 they grow in both the closed and open arms in sugar broth, and Maze^ found that while it is 

 the oxidation by free oxygen that furnishes the energy necessary to the aerobic multiplica- 

 tion of yeasts it is the splitting of sugars into acetic acid that furnishes the energy for their 

 anaerobic growth. 



It is by no means certain that obligate anaerobes require an absolute exclusion of 

 oxygen for their maximum growth; but certainly the amount necessary to inhibit 

 growth is very small, according to Matzuschita,^ for certain anaerobes about 0.0031 

 per cent.^ 



Many anaerobes seem to grow best at or near the limit of oxygen tolerance. Engle- 

 mann,7 by observation of the chemotactic behavior of motile bacteria with respect to 

 the oxygen secreted by a living filament, and Beijerinck,* by observing the levels at 

 which bacteria grow in deep media, showed that different anaerobes vary in their 

 oxygen requirements. Chudiakow' and Fermi and Bassu'" also concluded that even 

 the anaerobic bacteria require some free oxygen, but if this be so the amount is so 

 small for the obligate anaerobes that it is practically impossible to measure it. And 

 no one has ever been able to establish the minimal oxygen requirement, if there is any 

 such thing, for any strict anaerobe. 



Yet the conception of maximal, optimal, and minimal oxygen tensions has a dis- 

 tinct place in connection with the "micro-aerophiles" of Beijerinck,* and in the sporu- 

 lation of aerobes as shown by A. Meyer." 



■ Mathews, A. P.: Biol. Bull., 8, 331. 1905. ' Packard, W. H.: loc. cit. 



3 Smith, T.: Centralbl.f. Bakteriol., Abt. I, Orig., 18, i. 1895. 



■•Maze, P.: Ann. del'InsL Pasteur, 18, 277. 1904. 



5 Matzuschita, T.: Arch.f. Hyg., 43, 267. 1902. 



' Cf. Clark, W. M.: chap, xii of this volume. 



'Englemann, W.: Botan. Ztng., 39, 442. 1881. 



*Beijerinck, W. M.: Centralbl.f. Bakteriol., Abt. I, Orig., 14, 827. 1893 



»Chudiakow, N.: ibid., Abt. II, Orig., 4, 389. 1898. 

 "> Fermi, C, and Bassu, E.: ibid., Abt. I, Orig., 35, 563 and 714. 1904. 

 "Meyer, A.: ibid., 49, 305. 1909. 



