Originally published in the Scientific Monlhlij 83, No. 5 (1956) 



25. PATH OF ATOMS THROUGH GENERATIONS 



G. Hevesy 

 From the Tnstitut for Research in Organic Chemistry, Stockholm 



The number of atoms inherited from the mother whicii is passed on to 

 the next generation depends on three factors: (i) the fraction of the 

 total number of atoms of the mother which were passed on to the newly 

 born; (ii) the number of inherited maternal atoms that are replaced 

 ))efore birth of the grandchild by atoms from nutrients; and (iii) the 

 number of maternal atoms still present at pregnancy which can be used 

 for development of the embryo of the next generation. 



The quantity mentioned first depends essentially on the weight ratio 

 between the mother and the newly born. Sodium, chlorine, and sulfur 

 are preferred by the body of the newly born, whereas potassium, calcium, 

 magnesium, and phosphorus are preferred by the body of the mother. 

 The greatest discrepancy from an equilibrium distribution is seen in 

 calcium. The concentration of calcium is about 3 times larger in the 

 body of the mother than in the body of the newly born. The reason for 

 this is the calcium deficiency of the developing skeleton of the newly born. 



The loss of inherited atoms before reproduction of the animal and the 

 stability of the still-present, inherited atoms for the development of the 

 embryo of the next generation vary decidedly from element to element. 



It has long been recognized that food supplied to the body is not 

 only used to supply energy but is also of great importance in the replace- 

 ment of used parts of the body. However, only in the last decades has 

 interest begun to develop in the quantitative side of the second function 

 of the nutrients and in determining the lifetime of molecules and atoms 

 in the bodies of animals and plants. 



REPLACEMENT OF SODIUM ATOMS OF THE BODY 



As the first example for the replacement of atoms present in the body 

 by atoms absorbed from food, we shall consider the fate of the sodium 

 atoms in the organism. If radioactively labelled sodium— for example, 

 in sodium chloride — is supplied to the body, the supplied sodium ions 



