Physiology. — “About the influence of radio-active elements on the 
development’. By Prof. A. J. P. van pen Brork. (Communi- 
cated by Prof. H. ZWAARDEMAKER). 
(Communicated at the meeting of November 29, 1919). 
One of the elements, composing the living protoplasma, potassium, is 
radio-active. The investigations of ZWAARDEMAKER and his pupils about 
the signification of potassium in the organism have proved that, chiefly 
by streaming experiments of the isolated frog-heart, potassium can be 
substituted by an aequiradio-active quantity of any other radio-active 
element. 
On account of this ZWAARDEMAKER concludes‘): ‘die Radioaktivitat 
und keine andere Eigenschaft der sich gegenseitig vertretenden Atome 
erfüllt die für die Automatie notwendige Bedingung” (Le. pag. 49). 
Next to this substitute ZWAARDEMAKER has fixed the attention on a 
second fact, viz. an antagonism between different groups of radio- 
active elements. 
The antagonism is expressed in the following scheme: 
Uranium 
Potassium | Thorium 
Rubidium > _ Radium 
(Casium) = Ioniam 
Niton (Kmanation) 
The uranium substitutes the potassium in certain experiments; but 
the elements together neutralize each others’ effect. 
These investigations raise the question if it were possible to sub- 
stitute the potassium during the development by another radio-active 
element. | tried to obtain an answer on this question by experimental 
investigation. I will give a short account of the experiments taken 
and of the results which [ obtained. The experiments were taken 
with frog-eggs and carried out in the following way. 
After the fecundation (in the laboratory) the egglump was parted 
') H Zwaarpemaker, Die Bedeutung des Kaliums im Organismus. Pllügers’ 
Archiv. Bd. 173. 
