Physiology. — “On Sensibilization to Radioactivity by the action 
of Hormones”. By Prof. H. ZWAARDEMAKER. 
(Communicated at the meeting of Sept. 25, 1920). 
Sensibilization of organisms or organs to the energy of light has 
long since been a familiar process in physiology. It is especially 
H. von Tappriner') who has called attention to some fluorescent 
substances, which in the presence of oxygen largely increase the 
deleterious influence of light. This noxious influence resembles the 
influence of ultraviolet rays. Mr. and Mrs. Henri’) have detected 
likewise an action of the colloidal selenium for the ultra-violet rays. 
Long afterwards similar effects have been detected for the Röntgen- 
rays. This is instanced by the use of enzytol (10°/, solution of boric 
acid cholin) to increase the destruction of malignant tumors in 
Röntgenization *) 
In 1917) I have established sensibilization for Becequerel-rays. 
Here also there were fluorescent substances which brought it about, 
to wit fluorescein and eosin. The former had the stronger action 
for the a-rays, the latter for the 3-rays. Their action took place 
irrespective of the presence or the absence of light. In virtue of 
standard experiments with adsorbentia (e.g. taleum venetum) I 
correlated the sensibilization in these cases with a reinforcement of 
the adsorptions, which the radioactive ions undergo through the 
action of the sensibilizers. In these experiments we found a super- 
session of fluorescein adsorption by eosin and not the reverse, running 
parallel to a supersession of the sensibilization of fluorescein by 
eosin and not the reverse‘). In general the adsorptions play a 
prominent part in the action of radio-active atoms of the circulating 
fluids, because the ions, moving freely in the fluid, exert an influence 
!) H. von TAPPEINER, die photodynamische Erscheinung (Sensibilisierung durch 
fluoreszierenden Stoffe). Ergebnisse der Physiol. Bd. 8. S. 698. 1909. 
*) M. er Me. Victor Henri, Action photodynamique du sélénium colloidal, Soc. 
de Biologie. C. R. du 24 févr. 1912. R 
8) A full list of the literature on cholin-action is to be found in Dorn Strahlen- 
therapie Bd. 8. S. 499. 
*) Kon. Akad. v. Wetenschappen, Amsterdam 27 Sept 1917. 
5) See for the technique A. M. SrreeF, Onderz. Physiol. Lab. Utrecht, 5e Reeks 
XVIII p. 59. 
