1161 
larval instars, which represent secondarily introduced phases of 
development. 
On quite different grounds the same assertion has been defended 
by DrrGcenrer (1909). 
Considering the regular occurrence of a macula dorsolateralis on 
the pupa situated between m. dorsalis and m. suprastigmalis (even 
when a seta dorsolateralis is wanting on the abdominal segments 
of the larva), the pupa may be said to have best preserved the 
original hexapodal colour-design of the insect, at least in this in- 
stance and in the ornamentation also the thoracic segments which 
in other respects have been so profoundly modified. 
The Hague, March 1917. 
Physiology. — “ Distance-relations in the Effects of Radium-radiation 
on the tsoluted Heart’. By Prof. H. ZwAaRDEMAKER. 
(Communicated in the meeting of March 31, 1917). 
The results of 34 initial experiments '), justified the present writer 
in establishing that an isolated frog’s hart, fed after KRONECKER’s 
method with Rincer’s mixture deprived of potassium chloride, resumes 
its beats again after, a standstill wben exposed to the radiation of 
mesothorium or radium. *) We used 6 mgrms of mesothorium 
enclosed in a glass bulb and 3 mgrms of radiumbromide under 
mica. On an average an exposure of half an hour was required for 
the restoration of the pulsations. *) 
Then however a good and regular contraction recommenced, 
the rhythm being about the same as when the heart was not yet 
freed from the circulating potassium. The mesothorium-tests were 
also successful when the rays had to pass through an aluminium 
screen 0.2 mm. thick. 
In the meeting of February I could also demonstrate that potas- 
sium and rubidium, when either of them is contained in the 
il) H. ZWAARDEMAKER, C. E. BENJAMINS and T. P. Feenstra, Radium-radiation 
and cardiac action. Ned. Tydsch. v. Geneesk. 1916 Il p. 1923. 
*).The previous removal of potassium from the circulating fluid is very essential, 
for exposure of the heart in situ or perfused with normal Runcer’s mixture, does 
not alter the actual beats materially. 
5) The intervals between the commencement of the exposure to radiation and 
the recurrence of pulsation differ very much. They depend on the velocity of 
perfusion, the natural frequency of pulsations, the time the inactive circulating 
fluid needs to cause a standstill, etc. 
