98 Prof. W. Pfeffer. The Nature and 



for oxygen-respiration are absent. Thus, in the case of facul- 

 tative anaerobes, in proportion as oxygen becomes deficient, aerobic 

 becomes replaced by anaerobic metabolism, while the obligatory 

 anaerobes now for the first time begin their growth and multiplica- 

 tion. This is correlated with the fact, that oxygen, even at low 

 tension, acts as a poison to them, and when air is so much com- 

 pressed that the oxygen is twenty or thirty times as dense as in 

 the atmosphere, all plants perish. All gradations of sensitiveness 

 towards oxygen occur, from the most resistant organisms down- 

 wards, and there are even obligatory aerobes, such as the sulphur- 

 bacteria, which can only exist when oxygen is of very low density. 



Thus the different types are connected by intermediate links. For 

 any facultative anaerobe it is possible to prepare a nutritive sub- 

 stratum on which it can nourish only when able to respire free 

 oxygen. If, however, the oxygen be presented in sufficient dilution 

 it does not hinder the growth of the anaerobic organism, which, 

 under these circumstances, constantly draws the free oxygen into its 

 functional metabolism, and thus gradually consumes it in considerable 

 quantities. Further, a variable density of the free oxygen may be 

 endured by the same organism in accordance with the cultural condi- 

 tions under which it is placed. It has in fact been found possible, by 

 means of special nutrition, to cultivate the strictly anaerobic Bacillus 

 of symptomatic anthrax (B. carbonis) as an ae'robe. The habits of tho 

 nitrogen-assimilating Clostridium Pasteurianum are also evidently 

 modified by certain bacteria which usually live associated with it, 

 for in such svmbiosis Clostridium endures the free access of air, 

 while in the isolated condition it can only live anaerobically. 



Even in the case of typical aerobes, however, the withdrawal of 

 oxygen does not bring the metabolic activity entirely to a standstill. 

 At first carbonic acid is still given off, being derived from the 

 intramolecular respiration, i.e., from chemico-physiological processes, 

 which in most plants further result in the formation of alcohol and 

 other products. This intramolecular respiration is thns a vital 

 action which is of importance for the maintenance of life even in 

 aerobes, but which in the latter does not suffice to maintain the whole 

 working of the organism after oxygen has been withdrawn. In the 

 anaerobes this capacity has been fully developed, but of course only 

 comes into play when suitable nutrition is provided. For, when differ- 

 ently fed, even the facultative anaerobe can only grow if fully supplied 

 with air, and behaves, when oxygen is withdrawn, just like a typi- 

 cally aerobic plant, for it then ceases to grow, and, sooner or later, 

 perishes altogether. By means of an appropriate food-mixture, 

 however, we can ensure that the facultative anaerobe continues its 

 growth and movements, but only for a certain time and to a certain 

 extent, thus appearing as a temporarily anaerobic organism. Such 





