VITAL GROWTH AND CRYSTALLIZATION 



31 



calculated the stress lines in it, according to the mechanical 

 principles well known to him. In this calculation he took 

 into account the effect of the load of the human body. In 

 brief he devised a structure resembling a crane, with the 

 well-known outline of the thigh bone, which was capable of 

 meeting the required stresses. On comparing this con- 

 structed system of lines and planes with the distribution of 

 the bony material in the bones, a complete agreement was 

 found (Fig. 15). 



Fig. 15. Stress Lines in the Thigh Bone 



Diagram A gives an idea of the location of the lines of stress in the head 

 of a crane, diagram B those on the surface of the femur. 



This stripe formation in bony material is quite com- 

 parable to the stripes formed in gelatin under stress. It is 

 assuredly worth noting that we can learn something about 

 the make-up and character of vital structures from these 

 simple experiments with gelatin or egg white. It serves as 

 encouragement to investigate the matter on a somewhat 

 wider scale. A more systematic survey shows that gelatin, 

 or salts crystallizing in it, and various soft and slimy mate- 

 rials, such as starch, when crystallizing under differing con- 

 ditions, give rise to an enormous number of forms. Some 

 of these forms bear a truly surprising likeness to certain 

 living forms (Figs. 16-22). 



