CHEMICAL CRITERIA OF ANAEROBIOSIS 35 



which transfer gases absorbed at the au* surface to the oil-medium 

 surface. Such convection cm'rents are absent, of course, in the 

 sohd waxes and semisohd greases. 



These researches would be barren were we not able to afifirm 

 the parallelism of cultural studies. As a matter of fact, dilution 

 experiments with such organisms as B. tetani, B. Welchii, B. 

 sporogenes and others confirm the great value of paraflfine and 

 vaseline as compared with liquid mineral oil. B. tetani absolutely 

 failed to grow under either xylol or heptane, gave only delayed 

 turbidity under mineral oil and vigorous early gas production 

 under paraffine. Yet none of these is germicidal for B. tetani 

 as shown by successful growth under the marble in a constricted 

 tube of glucose broth covered with them. 



The great objections to vasehne and parafRne are their mess- 

 iness and the fact that they do not provide sufficient variety 

 of oxygen pressures in the medium to meet the possible require- 

 ments of different organisms. 



Boihng as a means of oxygen tension reduction is sometimes 

 used in methods where the air chamber is sealed either by fusion 

 of the glass outlet or by mechanical devices such as valves, 

 cocks, etc. Either method is satisfactory from the standpoint 

 of the persistence of the decolorized state of methylene blue 

 but is obviously superfluous for deep cultures and is inapplicable 

 to surface cultures for reasons easily apparent. 



Evacuation by water pump to 58 cm. mercurial pressure with 

 immediate sealing of a constricted portion of the tube has never 

 sufficed to decolorize methylene blue 1:100,000 either with 2 

 per cent glucose and n/500 NaOH or 2 per cent agar and n/100 

 NaOH at ordinary room temperature in our hands. Nor have 

 we ever been able to secure surface growths of such obligate 

 anaerobes as B. Welchii, B. tetani, B. oedematis and B. botulinus 

 on the surface of solidified glucose agar by this means alone. 

 We are therefore forced to conclude that evacuation by water 

 pumps of such efficiency is of relatively little value alone as a 

 method of securing anaerobiosis. Higher evacuation might 

 yield more successful results. 



