102 RADIO-ACTIVITY 



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 

 radio-active 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 electrons (^ 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 : 



(1) Because of its velocity, the ^ ray accelerates the rate of 

 migration of gaseous ions in a similar way to ultra-violet light 

 of extremely short wave-length (below 2,000 Angstrom units), i.e. 

 the gas becomes an electrical conductor. 



(2) On account of its unit negative charge, it has a disturbing 

 effect on all systems in electrical equilibrium through which it 

 passes. 



Rutherford has recently shown that a particles (positively 

 charged nuclei of helium, atomic weight — 4) may cause trivalent 

 nitrogen (14) to disintegrate with the formation of monovalent 

 hydrogen (1). He considers that the hydrogen ion is a unit 

 positive charge. Other atoms are composed, as we have seen, of a 

 positively charged nucleus about which are grouped sufficient 

 electrons to render the whole system neutral. 



The modern tendency is thus to postulate the sameness of all 

 elementary matter. What we have been accustomed to look 

 upon as elements may merely be stages in the disintegration of 

 more complex substances into their positive and negative units. 

 When the disintegration takes place explosively and continuously 

 the substance is considered as radioactive. 



In the preceding portion of this chapter, kathode rays, X-rays 

 and the a, j8, and y rays of radio-active inatter have been mentioned 

 as types of radiation. These various radiations differ from one 

 another in their effects on living matter in degree rather than in 



