122 RADIO-ACTIVITY 



Subsequent investigations by the above workers, and principally 

 by Rutherford, Soddy, and their collaborators, have shown that 

 there are three series of radio-active elements. The appended 

 chart from Soddy shows the relationship between the members 

 of the series and between two of the series themselves. This chart 

 demonstrates to us the remarkable fact that the atom of the 

 heavy elements at the head of each series are continuously and 

 regularly undergoing disintegration. Matter and energy are being 

 lost at a rate which, so far, cannot be modified in any way. 



Lately Campbell and Wood have discovered that certain of the 

 elements of low atomic weight are also radio-active. One of 

 these, potassium, is found universally and in abundant quantities 

 in animal and vegetable cells. Potassium is a necessary per- 

 manent constituent of every living cell. Of the 12-15 elements 

 essential to life, it is the only one possessing distinct if minute 

 radio-activity. The activity of potassium may readily be demon- 

 strated by means of the gold-leaf electroscope. It is shown that 

 P rays are emitted. Potassium is 1000 times weaker than uranium 

 and 1,000,000,000 times weaker than radium in the emission of 

 /3 rays. 



As is well known, potassium is an absolutely necessary con- 

 stituent of the fluid used for the perfusion of an organ. If a 

 potassium-free Ringer's fluid is passed through a frog's heart, the 

 heart will come to a standstill in about half an hour. The frog's 

 peripheral vessels may be perfused with Ringer's fluid for hours 

 without any sign of oedema. As soon as a potassium-free fluid 

 is used, marked oedema begins, causing the frog to swell and 

 increase in weight. Further, the frog's kidneys when perfused 

 with Tyrode's fluid or similar fluid containing glucose allows no 

 glucose to pass out into the urine. If the potassium is omitted 

 in making up the fluid, glucose at once escapes into the urine. 

 Ringer demonstrated, long before its radio-active nature was 

 discovered, that rubidium may be substituted for potassium in 

 equimolecular amounts. He explained this by its similar chemical 

 nature. Similarly, caesium, another of the lighter radio-active 

 elements, may take the place of potassium in the perfusion fluid. 

 No non-radio-active element has been found which is capable of 

 acting as a substitute for potassium. Further, Zwaardemaker 

 was able to perform normal perfusions provided a substance 

 emitting /5 rays was within effective distance of the frog. 



The last named worker and his collaborators then set out to 

 determine the amounts of the heavy radio-active elements necessary 



