G. S. Graham-Smith 
39 
growths. As growth continues the distal ends of the newly formed 
bacilli very gradually approach each other, but the organisms seldom 
become parallel. 
M 
Diagram 8. Illustrating the development of various diphtheroid organisms 
on the surface of agar. 
Hill (1901, p. 81) offers the following hypothesis in explanation of 
these movements. “ That the visible bacterial rod is surrounded by an 
invisible or scarcely visible membrane ; that in B. diphtheriae (and 
other members of this group) only incomplete rupture of this membrane 
after fission occurs, the line of rupture running round only a portion of 
the circumference of the original rod, leaving a bridge connecting the 
new rods formed; that the enlargement of these rods before snapping 
and the tension thus produced originate the rupture ; that the snapping 
is due to the sudden occurrence of the rupture, and that the preliminary 
angular position and the parallelism finally achieved are due to the 
