IVAN C. HALL 201 



Thus the problems of anaerobiosis are not limited to a single group of bacteria 

 but are shared by several groups, by protozoa, various invertebrates, and even by the 

 tissues of warm-blooded animals. While some of the invertebrate metazoa may live 

 as facultative anaerobes during all or part of their existence, the condition of obligate 

 anaerobiosis seems to be limited to single-celled micro-organisms, particularly the 

 bacteria and protozoa. Whether any of the ultra-microscopic viruses are obligately 

 anaerobic must await their certain culture in artificial media. It is of interest to note 

 that no obligately anaerobic yeasts or molds are known. 



MECHANISM OF BACTERIAL ANAEROBIOSIS 

 PHYSICO-CHEMICAL CONCEPTIONS 



Pasteur's explanation of anaerobiosis was that the organisms secure their oxygen 

 through the fermentation of carbohydrates. Certainly the growth of some obligate 

 anaerobes is dependent upon the presence of fermentable carbohydrates. This seems 

 to be the case with the actively saccharolytic species, B. butyricus, B. mnltifernientans, 

 B.fallax, and B. sphenoides, none of which possesses sufficient lytic ability against ni- 

 trogenous compounds to hydrolyze even gelatin. Certain other species, e.g., B. welckii, 

 B. chauvoei, B. septicus, B. novyi, and B. tetanomorphiis, grow, but poorly, except in the 

 presence of fermentable carbohydrates; these split gelatin and peptones but not native 

 proteins. But the actively proteolytic bacteria, such as B. bifermentans, B. tyrosino- 

 genes, B. aerofoetidus, B. botulinus, and B. sporogenes, grow quite heavily in sugar-free 

 media tliough not so heavily as in media containing fermentable carbohydrates 

 (mono-saccharides). Still other species, B. tetani and B. putrificus, though unable to 

 ferment any carbohydrate, still grow anaerobically ; both are mildly proteolytic. From 

 these considerations we may conceive that obligately anaerobic bacteria derive the 

 oxygen assumed to be necessary in their metabolism not only through the hydrolysis 

 of carbohydrates but also of nitrogenous compounds. 



Unless there is some essential difference in the mechanism of anaerobic growth of 

 facultative and obligate anaerobes, something may be learned about the latter by 

 studying the former. Pasteur^ showed that the products of fermentation of molds 

 and yeasts vary according to whether they are provided with oxygen, thus Mucor 

 racemosiis in the open air transforms glucose into CO2 and H2O, but in the absence of 

 air produces alcohol and CO2; in other words, oxidative processes fall short under an- 

 aerobic conditions. 



Until a few years ago, Hoppe-Seyler's theory of biological oxidation^ was most widely 

 accepted. According to him, fermentation results in the liberation of nascent hydrogen 

 which combines with atmospheric oxygen, forming water (H2+02 = H20-|-0), setting free 

 nascent oxygen which is directly responsible for oxidation in the protoplasm. But this theory 

 could not account for anaerobic respiration where oxidations occur in the practically com- 

 plete absence of free oxygen. Armstrong^ has shown that in ordinary oxidations free oxygen 

 does not unite directly with carbon to form carbon dioxide or with hydrogen to form water, 

 but any substance that is to be oxidized is first hydroxylated, atmospheric oxygen acting 



'Pasteur, L.: Eludes sur la Bicre. 1876. 



^ Hoppe-Seyler, F.: Ztschr.f. Physiol. Cliemie, i, 121. 1877. 



3 Armstrong, H. E.: Chem. A^eit's, 90, 25. 1904; Tr. Chem. Soc. London, 83, 1088. 1903. 



