124 RADIO-ACTIVITY 



to replace potassium. These radio-elements, as we have seen, 

 emit a rays in marked excess of the /? rays necessary for physio- 

 logical purposes. They found that, as was to be expected, the 

 a radiation completely masked the /5 radiation. If means were 

 taken to exclude the ft rays these a+/? radiating salts acted as 

 excellent substitutes for potassium. Radio-active substances 

 may thus be classified for biological purposes into two groups. 



TABLE XXI. 



I. 



/^Radiating (negative). 



Potassium. 

 Rubidium. 

 Caesium. 



II. 



a Radiating (positive). 



Uranium. 



Thorium. 



Radium. 



Ionium. 



Lanthanum. 



Cerium. 



Niton (Emanation). 



A heart beating with a fluid containing the appropriate quantity 

 of any of Group I. may be switched on to any other group I. 

 element in aequi-radio-active amounts. Similarly, the group II. 

 elements are interchangeable. But direct transference from a I. 

 fluid to a II. or vice versa at once produces complete stoppage. 

 The two groups are antagonistic. If, however, the heart is washed 

 completely free from one group with radio-active-free fluid it may 

 without harm be perfused with a fluid containing one of the 

 elements of the antagonistic group. 



Fluorescein and eosin adsorb the a and />' rays unequally. If 

 one of these dyes be added to the perfusion fluid the amount of 

 radio-active material present may be reduced appreciably and 

 still produce normal action. In summer, smaller quantities of 

 radioactive salts are needed than in winter. This is related to 

 the lowered calcium content in the frog's blood in winter. 



To summarise, potassium is a necessary constituent of all 

 living matter because of its property of emitting negative electrons 

 (/5 rays). It may be replaced by other radio-active substances 

 in aequi-radio-active proportions provided these substances are 

 not otherwise toxic. How potassium acts in the living cell can 

 as yet be only a matter of surmise. Presumably the freed electron 

 passing with great velocity through crowds of ions, molecules and 

 colloidal aggregates will have some effect on them. It is known 

 to have at least two effects : 



