Wetting on Pathogenicity of Tubercle Bacillus 231 



1 per cent, castor oil soap solution, and making cultures at given 

 intervals. The organisms which were thus transferred from the 

 soap solution to glycerine broth sank to the bottom of the flask 

 immediately and there was no growth even after a prolonged 

 period of incubation. If, however, the cultures were made on the 

 surface of egg medium, or supported in the surface of glycerine 

 broth by means of a wire gauze, growth developed with charac- 

 teristic pellicle formation. 



From this experiment we conclude that, under these experi- 

 mental conditions, the pathogenic properties of the tubercle bacilli 

 are lost before the property to reproduce. The fact that we ob- 

 tained growth in the above experiment when the organisms were 

 supported in the surface of the glycerine broth, and a negative 

 culture when the inoculun fell to the bottom of the flask will be 

 attributed by most bacteriologists as due to the influence of 

 oxygen. Bacteriologists have for years considered pellicle growth 

 as evidence of obligatory aerobiosis. But those who hold to this 

 view have not offered an explanation as to the force which sup- 

 ports the organisms on the surface of a liquid medium. 



With few exceptions most pellicles may be sedimented by 

 slight agitation or centrifugation. 



This indicates clearly that they are of higher specific gravity 

 than the medium upon which they are growing. It follows there- 

 fore that they are supported on the surface of a fluid medium 

 by some force. Since ''demand for oxygen" is not a force it fol- 

 lows further that they are not on the surface because of their 

 demand for oxygen, although the oxygen present may, un- 

 doubtedly does, influence their development. The fact that 

 tubercle bacilli will grow diffusely through the medium by ap- 

 propriately depressing its surface tension is evidence that it will 

 grow under conditions where the oxygen tension is not at its 

 maximum. Its tendency to grow only in or upon the surface 

 of glycerine broth is probably due to the concentration of surface 

 tension depressants there, which create optimal conditions of 

 wetting. 



The foregoing observations suggest that an important func- 

 tion of the fat in the cell membrane is to regulate the "wetting" 

 of the cell. 



Since glycerine is the carbon compound par excellence from 

 which bacteria synthesize fats, as shown by Larson and Larson, 4 



