CELLS OF THE COLON BACILLUS 95 



i.e., while a rigid cell wall may maintain a form other than the 

 spherical, it cannot give rise to it. Frobisher suggests that with 

 bacteria, since they elongate perceptibly without changing in diame- 

 ter, the rigid cell wall, if it exists, may be open at the ends. The 

 fact that the ends of cells where they are not in contact with 

 contiguous cells are always rounded supports this view. 



If the elongated form of the cells is due to some internal, axially 

 disposed force, opposing the rounding effect of surface tension, then 

 when placed in a medium of lowered surface tension, this force 

 meeting less opposition should produce a more pronounced effect, 

 and the cells should become even longer and more slender. This 

 in fact is what occurs. Frobisher noted that the morphologic varia- 

 tions induced by adding surface tension depressants to the medium 

 were comparatively slight, but that with low tensions (35-40 dynes) 

 the cells became longer and more slender. He observed but slight 

 variation because he was dealing with cells which had passed the 

 maximum growth phase. In some as yet uncompleted observations* 

 on the effect of sodium ricinoleate upon the size and form of the 

 cells of the colon bacillus, the soap being added in excess to agar, 

 I have found that whereas after twelve hours or so the cells were 

 only somewhat longer and more slender than in control cultures, 

 during the active growth phase (three to five hours) they were 

 astonishingly elongated and filamentous in form, many cells extend- 

 ing over several oil immersion fields. On the other hand, when cal- 

 cium chloride (which tends to raise the surface tension somewhat) 

 is added to the medium, the cells are somewhat shorter and more 

 oval in form than in the normal medium. 



If it be granted then that the elongation of the cells (with cor- 

 responding increasing slenderness) is due to the effect of some in- 

 ternal force opposing the surface tension of the medium, then we 

 must assume that this force is greater during the period of increasing 



* These experiments are uncompleted and are not reported in detail here 

 because of the technical difficulties involved. It is impossible to determine the 

 surface tension of agar after it has jelled, and difficult to obtain clear morpho- 

 logical studies from liquid media. The colon bacillus becomes strongly clumped 

 in the soap medium so that it is impossible to obtain accurate measures of 

 growth by any method. The growth forms a slimy mass which does not 

 stain readily and which is difficult to spread in thin films. 



