84 BIOLOGY AND SOCIAL PROBLEMS 



are, they are far from molecular limits, for 

 Von Frey has calculated that the extremely 

 minute amount of mercaptan which we can 

 just smell contains ahout a fifth of a billion of 

 molecules. Nevertheless, as compared with the 

 smallest amount of material that the physi- 

 cist or chemist can weigh directly and accu- 

 rately, namely, about 0.001 of a milligram, the 

 amounts of the various materials just men- 

 tioned are undeniably small. 



We have thus seen how each human being 

 starts life from a minute egg cell charged with 

 an infinitesimally small amount of material 

 which is destined to determine with surprising 

 accuracy his configuration and responsiveness. 

 The process that the egg cell undergoes in 

 changing into an adult person is first of all 

 cell division. The simple spherical egg cell di- 

 vides by a somewhat complex process into two 

 cells, and these into four, and so forth, till 

 the millions upon millions of cells which con- 

 stitute the adult body are formed. At each di- 

 vision the chromosomes divide and are shared 

 by the descendant cells so that both maternal 

 and paternal influences are handed on to each 

 cell in the growing individual. The great ag- 

 gregate of cells which thus constitute the adult 



