300 Blackman . — Radio-activity and 
of all living organisms, so that the question naturally arises of the impor- 
tance in normal physiological processes of the /3-particles, or electrons, which 
are continually being shot off from the atoms of potassium. In 1915 
H. Zwaardemaker, a Dutch worker, took up this question in relation to 
animal physiology and carried out a number of observations. He has 
recently given in English an account of his work in the ‘ Journal of Physio- 
logy ’ (vol. liii, p. 273-89, Feb. 1920). As his results are of fundamental 
importance for plant as well as animal physiologists, it seemed important 
that some brief resume of them should appear without delay in a botanical 
journal. 
Potassium in a quantity of about 40 grin, is found in the human body 
and is also an important constituent of the blood, where it occurs in the 
ionic state, the amount being estimated at about 1 grm. The importance 
of potassium for the beat of the heart is easily shown by experiments on the 
frog’s heart. If the heart is supplied with Ringer’s solution (NaCl 0-67 per 
cent., NaHC0 3 0*02 per cent., CaCJ 2 0*02 per cent., KC1 o*oi per cent.) 
it will beat for hours ; if the potassium is omitted from the solution the 
pulsation ceases in about 30 minutes. Zwaardemaker took advantage of 
this well-known fact to obtain information as to how far the action of the 
potassium ion is to be referred to its radio-active power. 
It was shown many years ago that rubidium could replace potassium 
in Ringers fluid, but these two elements are not only both radio-active but 
chemically very similar, so that such a result throws no light on the problem 
in question. If, however, potassium could be replaced by a radio-active 
element of entirely different chemical nature, such as one of the heavy 
radio-elements, the physiological importance of radio-activity would be 
demonstrated. Zwaardemaker therefore set himself to determine if sub- 
stances like radium, uranium, and thorium could replace potassium in 
Ringer’s fluid. One difficulty is that of the concentration of the substance 
that is to be used, for, clearly, what is required is not equivalent molecular, 
or ionic, concentration, but what Zwaardemaker calls ‘ aequiradio-activity ’. 
Rutherford has determined the intensity of the physical radio-active effects 
of the various radio-elements, and from these data the required strength of 
the substance to be used was estimated. Potassium, as already stated, emits 
/3-rays of only one-thousandth the activity of the /3-rays of the same quantity 
of uranium ; radium again is io~ 9 times as active in this respect as potassium. 
From such data Zwaardemaker calculated the amount of radio-element 
to be added to the Ringer’s fluid to expose the heart-muscle to the same 
intensity of radiation by /3-rays as when the normal potassium is used. 
Armed with this knowledge, Zwaardemaker in 1917 succeeded in demon- 
strating that uranium, thorium, and radium, when added in aequiradio-active 
quantity, can replace potassium in Ringer’s fluid, not only enabling the 
heart to continue beating, but restoring the pulsation of a heart which has 
