RELATION TO OXYGEN AND OTHER GASES. 43 



origin is usually not known. (Compare special part, Bac. 

 tetani, Bac. chauvoei. ) 



Not infrequently varieties are observed which show 

 more or less anaerobic growth when first isolated (growing 

 especially in the deep part of the agar stab), and which 

 later present a pure aerobic behavior i. e. , distinct sur- 

 face growth and poor growth along the stab. Thus, one 

 may properly speak of an adaptation to a gas-mixture, 

 rich in, or free from, oxygen, and in this way may ex- 

 plain very many things. 



These observations prove to the classifier that bacteria 

 can not be thus simply separated into two classes, the one 

 aerobic and the other anaerobic. 



Recently the fact has been repeatedly demonstrated that 

 true anaerobic varieties also grow well without the exclu- 

 sion of oxygen, if they are associated with many aerobic 

 varieties; also that for the aerobic growth of anaerobic vari- 

 eties, often nutrient media suffice if aerobic bacteria have 

 previously grown in them and have been killed with chloro- 

 form before the anaerobe is inoculated (Kedrowski, 

 Scholz). The synergetic aerobic variety evidently oper- 

 ates in part by consuming the oxygen, in part by pro- 

 ducing materials required by the anaerobic varieties. 

 Trenkmann recognized such a substance in sodium sul- 

 phid. Two drops of a 10% solution of sodium sulphid 

 render bouillon suitable for the growth of anaerobic varie- 

 ties without the exclusion of oxygen (C. B. xxm, 1038). 



While, besides the obligate anaerobes, all facultative 

 anaerobes thrive well in nitrogen and hydrogen, they vary 

 in their toleration of C0 2 . (Compare Table I, at end of 

 book. ) 



A large number do not thrive at all, and remain completely inhibited 

 in their growth until oxygen is again admitted ; for example, B. an- 

 thracis, subtilis, and related varieties. It is established regarding 

 some varieties (anthrax, cholera) that most of the individuals are rap- 

 idly killed by CO 2 , while some germs exhibit energetic resistance, and 

 render a complete sterilization by CO ? impossible. A second group 

 presents a restricted growth, especially if the test is carried on at in- 

 cubator temperature (staphylococci, streptococci), while a third group 

 is not injured at all: B. prodigiosum, B. acidi lactici, B. typhi. They 

 grow as well as in air; the liquefaction of gelatin is not interfered 

 with, but naturally, from the exclusion of oxygen, chromogenesis is 

 checked. Moreover, a mixture of 25% air and 75 $> CO 2 has no 



