THE VITAL CONDITIONS OF BACTERIA. 97 



have shown that aerobic races exist among the anae- 

 robic varieties. 



It is observed not very rarely that varieties which 

 on isolation exhibited more or less anaerobic growth 

 (for example, grew chiefly into the depth of the agar 

 stick canal), in time manifest a purely aerobic con- 

 dition, i.e., distinct growth upon the surface and 

 dwarfed growth in the canal. 



These observations show that two varieties cannot 

 be distinguished from one another by simply calling 

 one aerobic, the other anaerobic. 



In addition to the strict anaerobics all the faculta- 

 tive anaerobic varieties thrive well in nitrogen and 

 hydrogen, but they tolerate carbonic acid in various 

 ways. 



A large number do not flourish at all, but their 

 development is entirely checked until oxygen is again 

 supplied for example, bacillus anthracis, bacillus 

 subtilis, and allied forms. Of several varieties (an- 

 thrax, cholera) it has been ascertained that the major- 

 ity of individuals are killed very quickly by carbonic 

 acid, while certain ones offer a very vigorous resistance 

 and render complete sterilization by CO 2 impossible. 

 A second group exhibits especially when the ex- 

 periment is made at incubating temperature feeble 

 growth (staphylococci, streptococci), while a third 

 group is not at all injured (bacterium prodigiosum, 

 bacterium acidi lactici, bacterium typhi). These 

 grow as well as they do in the air, and the liquefac- 

 tion of the gelatin is not interfered with. As a matter 

 of course, pigment is not formed on account of the 

 absence of oxygen. A mixture of twenty -five per cent 

 air with seventy-five per cent carbonic acid exerts no 

 7 



