SPIRAL TWIST AND OPT. ACTHITY 83 



of Sciences in Moscow, the dextral form was found only 

 three times, though numerous isolations from different 

 soils were made. 



The dextralitj" and sinistrality in Bacillus mycoidcs is 

 a hereditar}^ feature. Dextral forms are always obtained 

 from dextral forms, and sinistral from sinistral ones. 



It can be shown that the spiral form of the colonies of 

 this organism is a secondary feature which is the result 

 of the primary spiral structure of the growing cells which 

 constitute the filaments. If one stains the filaments on 

 the surface of the agar with neutral red or with toluidin 

 blue (1:5000) and examines them under the microscope, 

 one can occasionally observe the twisting of two filaments 

 which have encountered each other. The motion of the 

 growing filament consists of two components : an elonga- 

 tion and a rotation around the axis of the filament, these 

 will result in a spiral motion. Similar observations have 

 been made also by Stapp and Zycha (1931) and by Eob- 

 erts (1938). If during the free growth of a filament on 

 the agar surface, the filament rotates around its longitu- 

 dinal axis counter-clockwise, the interaction of the firm 

 surface of the agar and of the growing filament will cause 

 the latter to follow a spiral path in a counter-clockwise 

 direction. Consequently, the secondary sinistral coil of 

 the growing colony of bacteria will arise as a result of the 

 primary sinistral spiral growth of the cells of the fila- 

 ment. This is confirmed by the fact that a certain con- 

 sistency of culture medium is necessary for the typical 

 spiral growth of colonies (Pringsheim and Langer, 1924; 

 Hastings and Sagen, 1933). The latter authors state that 

 on agar of usual strength the growth of Bacillus my- 

 coides spreads from the place of inoculation in the form 

 of coarse filaments which twist counter-clockwise, form- 

 ing a symmetrical pattern. On less consistent agar this 

 pattern does not appear or is diffuse. 



3. Morphological Dissymmetry and Morphological In- 

 version in the Snail, Fruticicola lantzi. We shall consider 



