100 GENERAL PHYSIOLOGY 



by the subsequent discovery of previously unknown elements, 

 whose existence they had predicted from certain gaps existing m 

 the genealogical table of the elements. According to Wendt 

 ('91) and Prayer ('92), the elements have been developed in 

 the course of the earth's history by gradual condensation from a 

 primitive element, hydrogen, in such a way that those having a 

 higher atomic weight have been derived from those having a lower 

 one; finally, all have been derived from hydrogen, the element 

 possessing the lowest atomic weight. But here scientific theory 

 ceases and hypothesis begins. Whether hydrogen is really the 

 ultimate unit, and in what relation its atoms stand as ponderable 

 or mass-atoms to the imponderable universal ether, the existence 

 of which physics finds it necessary to assume from the phenomena 

 of light and electricity, for the present is not known. 



But if we confine ourselves to ponderable matter, to which 

 living substance, like all other bodies, belongs, chemical analysis 

 shows that of the sixty-eight elements of which the physical world 

 consists, twelve only are found constantly in living substance. 

 These twelve elements which occur in every cell are : — 



Name. Symbol. Atomic Weight. 



Carbon C 12 



Nitrogen N 14 



Sulphur S 32 



Hydrogen H 1 



Oxygen 16 



Phosphorus P 31 



Chlorine CI 35 



Potassium K 39 



Sodium Na 23 



Magnesium Mg 24 



Calcium Ca 40 



Iron Fe 56 



Besides these twelve general organic elements, a small number 

 of special elements occur which are not met with in all cells, and 

 some of which are found only very sporadically. These are : — 



Name, Symbol. Atomic Weight. 



Silicon Si 28 



Fluorine Fl 19 



Bromine Br 80 



Iodine I 127 



Aluminium Al 27 



Manganese ... Mn 55 



Among these, silicon is wide-spread and fluorine is infrequent, 

 while the others, which likewise have a very limited occurrence, 



