106 PRINCIPLES OF BACTERIOLOGY 



on the contrary, are very resistant. Anaerobic bacteria being deprived 

 of oxygen the chief source of energy supplied to the aerobic species, 

 by which they oxidize the nutritive substances in the culture media 

 they are dependent for their nutrition upon decomposable substances, 

 such as grape-sugar, which on separating into two smaller molecules, 

 alcohol and carbonic acid, give out energy or heat. Anaerobic bacteria, 

 therefore, require for their cultivation, as a rule, media containing 

 glucose or some equivalent. 



3. FACULTATIVE AEROBIC AND FACULTATIVE ANAEROBIC BACTERIA. 

 The greater number of aerobic bacteria, including most of the path- 

 ogenic species, are capable of withstanding, without being seriously 

 affected, some restriction in the amount of oxygen admitted, and many, 

 indeed, grow equally luxuriantly in the partial exclusion of oxygen. 

 Life in the animal body, for example, as in the intestines, necessitates 

 existence with diminished supply of oxygen. Pigment formation almost 

 always ceases with the exclusion of oxygen, but poisonous products of 

 decomposition may be more abundantly produced. 



It is important to note that, according to recent investigations, it 

 has been shown that the aerobic development of the anaerobes may 

 be facilitated by the presence of living or dead aerobes. 



It has also been observed not infrequently that certain species which 

 on their isolation at first showed more or less anaerobic development 

 that is, a preference to grow in the depth of an agar stick culture, 

 for instance after a while seem to become strict aerobes, growing only 

 on the surface of the medium. This observation proves that the simple 

 fact of an organism showing aerobic instead of anaerobic growth is not 

 sufficient for its separation into a distinct species. 



While all facultative as well as strict anaerobes grow well in nitrogen 

 and hydrogen, they behave very differently toward carbonic acid gas. 

 A large number of these species do not grow at all, being completely 

 inhibited in their development until oxygen is again admitted for 

 example, B. anthracis and B. subtilis and other allied species. It has 

 been found in some species, as glanders and cholera, that the majority 

 of the organisms are quickly killed by CO 2 , while a few offer a great 

 resistance, rendering impossible complete sterilization by means of 

 this gas. Another group, again viz., streptococcus and staphylo- 

 coccus exhibits a scanty growth; while a third group, like the B. 

 typhosus and B. prodigiosus, is not at all affected, growing equally as 

 well in the presence of oxygen, and the liquefaction, even of gelatin, 

 not being interfered with; only, on account of the lack of oxygen, there 

 is no pigment formation. Finally, a mixture of one-fourth air to three- 

 fourths carbonic acid gas seems to have no injurious effect on bacteria 

 which cannot grow in an atmosphere of pure CO 2 . 



Sulphuretted hydrogen in large quantity is a strong bacterial poison, 

 and even in small amounts kills some bacteria. 



