44 Spikazines 



one reason or another. A more complete account 

 of them will be found in E. B. Wilson's book on 

 *^The Cell in Development and Heredity.'' 



It appears that spontaneous cell division can 

 be explained only on the basis of a heterogeneous 

 internal structure, such as is postulated by the 

 spirazine hypothesis. In order to convey as clear 

 a conception as possible of the underlying princi- 

 ples, a mechanical illustration will be used. In 

 Fig. 7a two clamps are applied to a rope and their 

 ends forced apart by means of jack screws. Let 

 us assmue that each screw is able to exert a force 

 of one gram, but that it takes three grams to tear 

 the rope. The structure in Fig. 7a will therefore 

 not divide of its own accord. Let us now add to 

 each end of this structure another rope clamp and 

 another pair of jack screws as shown in Fig. 7b, 

 these additional parts being identical with the 

 homologous parts of the original structure. Each 

 time when such additional units are added to the 

 ends of this structure the tension of the rope is 

 increased, so that eventually it will tear in two at 

 the center. If, now, Ave substitute a polypeptide 

 spiral for the rope, and double or triple junctions 

 for the clamps and jack screws, then we will have 

 conditions substantially as they exist in bacteria 

 or other simple forms of living matter. Growth 

 by assimilation of additional amino acid mole- 



