1044 
potassium chloride and 100 molecules of sodium chloride; also oxygen 
and a buffer to obviate a change of the reaction through lactic acid 
and similar acids, which has proved to be highly deleterious’). 
A few months ago I demonstrated with Mr. Frrnsrra’) that 
in such cireulating fluids potassium chloride can be replaced by 
uranium-, thorium-, or radium-salts. The same statement was 
formerly made regarding rubidium by Sypney Rincer®). I am now in 
a position to add that radium-emanation initially to the quantity 
of 100 Macnr-units is also one of the elements, which, as far as 
their physiological action is concerned, can be substituted for potas- 
sium. These facts induced us to ascertain whether radiation of 
mesothorium or radium could be applied for the same purpose. 
About 34 experiments made with the assistance of Messrs. BENJA- 
MINS and Frrnstra *) confirmed this supposition to the full. The 
same result has since been obtained in a number of subsequent 
experiments. 
Quite unexpectedly an analogy thus reveals itself between radiation 
and the salts of potassium, rubidium, uranium, radium (and its 
emanation), elements belonging to widely differing groups of the 
periodic system. The radio-activity, common to all, is no doubt the 
true cause of the similarity in action. The question immediately 
arises, what is the amount of energy concerned? This may be 
determined when the artificial circulating fluid contains, instead 
of 100 mgrm. of potassium chloride, 5.10-§ mgrm. of a radium- 
salt per litre. Assuming */,, cc. to flow through the beating heart 
every second, +4.10-7 erg of radio-active energy per second is 
carried into the organ. It may be supposed that part of this 
amount is adsorbed by the muscle cells and acts physiologically. 
Then, however, we approach the energy quanta, which are known 
to stimulate the sense-organs, when they are responded to by an 
end-organ specially intended for it*). Also the quanta of energy 
transmitted by artificial circulating fluids containing uranium- or 
thorium-salts, appeared in our experiments to be of the same order °). 
1) G. R. Mines, J. of the Marine Biol. Assoc. Vol. 9. Oct. 1911, p. 171. 
2) T. P. Feenstra, These Proc. XIX p. 99, XX 341 and 633. 
3) S. Rincer, Journ, of Physiol. Vol. 4, p. 370. 
4) H. ZwAARDEMAKER, L. E. Bensamins and T. P. Feenstra, On Radium-radiation 
and cardiac action. Ned. Tijdschr. v. Gen. 1916 Il, p. 1928. 
5) H. Zwaarpemaker, Erg. d. Physiol. Bd. 4, p. 452. 1905. 
6) By far the greater number of our experiments were performed on the so- 
called Kroneckered heart, but in many cases also the whole heart was experi- 
mented upon. 
