94 MORPHOLOGIC VARIATION 



acceleration the surface-volume ratio is decreased. It should be 

 pointed out, however, that while this is true as long as individual 

 cells are concerned, the reverse condition obtains when we consider 

 the total amount of protoplasm, a greater surface being presented 

 by a mass divided into small particles even if these be spherical, 

 than by the same mass divided into larger particles, even though 

 these are filamentous. These considerations indicate that we may 

 with advantage consider the variations of the cells both in size and 

 form from the standpoint of surface phenomena. 



"Among the forces which determine the forms of cells" says 

 D'Arcy Thompson, "whether they be solitary or arranged in con- 

 tact with one another, this force of surface tension is certainly of 

 great, and is probably of paramount importance." With organisms 

 as small as bacteria, where the surface in proportion to mass of 

 protoplasm is so greatly increased, this force must be, if possible, of 

 even greater importance than with larger cells; Thompson explains 

 in this way the relatively slight variation in form encountered with 

 bacteria as compared with higher organisms. While it would take 

 us too far afield (and require a much more extensive knowledge of 

 the subject than I possess), to discuss in all its details this relation- 

 ship of surface tension to the size and form of the cells of bacteria, 

 a word or two on the matter may well be interpolated here. For 

 a more detailed discussion of the matter, the reader is referred to 

 Thompson's work. 



If bacterial cells were at all times homogeneous masses of proto- 

 plasm, their cells should at all times be spherical, as with the cocci 

 in the resting phase. But since with all forms, including the cocci 

 when actively growing, the cells are elongated, there must be present 

 some axially disposed force, some polar distribution of substances 

 (and consequently of energies) to give them this oval or cylindrical 

 or filamentous form. It is known with higher organisms, and gener- 

 ally assumed with bacteria, that forms other than the spherical 

 are maintained by a certain rigidity of the cell wall due to the depo- 

 sition of solid substances there. But, of course, the cell must have 

 assumed its form previous to the deposition of this substance; conse- 

 quently something must have been opposed to the rounding effect of 

 surface tension previous to the development of rigidity in the wall; 



