633 
These data appear to us to clearly demonstrate that the inhibition, 
proceeding from the false recognition in the interval, exerted upon 
the recognition of the primary stimulus, manifests itself also in the 
reaction-times. A comparison of the latter in the case of false 
recognition with those for the figures, the alteration of which was 
recognized in the interval (Ll and II) reveals that this inhibition is 
not insignificant with each observer. This appears still more clearly 
from a comparison of the times of I and IV, since the figures, 
shown only at the first sitting, were not under the influence of in- 
hibition in the interval. 
The fact that the time, required for recognition, in the case of a 
recognized alteration in the interval (II) is much shorter than the 
time needed for a sensation of novel experience (III) evoked for 
the altered figure, is easily accounted for by the circumstance that, 
owing to the novel sensation evoked by the figure, the experiencing 
person could not associate this figure with the primary one, which 
he could indeed when recognition of the alteration occurred. 
Physiology. — “Radium as a Substitute, to an equiradio-active 
amount, for Potassium in the so-called physiological fluids ; 
an experimental investigation in collaboration with Mr. 
T. P. Feenstra, assistant at the Utrecht Physiol. Lab.” By Prof. 
H. ZWAARDEMAKER. 
(Communicated in the meeting of Sept. 30, 1916). 
Considering that potassium is the only radio-active element always 
present in the animal body, I suggested to Mr. T. P. Feenstra, 
about a year ago, to ascertain whether potassium could be replaced 
by other radio-active elements in non-toxic doses. It afterwards 
appeared that similar experiments had been performed on rubidium 
by S. RiNGer, after whom the physiologicai solutions, in use nowadays, 
are generally named, when he expressed the relation of all the salts 
of the MeNDELEJEFF-group (to which potassium belongs) to potassium 
salts, in equimolecular ratios. Mr. Feenstra, while abandoning the 
molecular ratios, followed quite a different method, viz. he measured 
the doses of his elements upon the basis of radio-activity, being 
fully alive to the responsibility for the view-point which he thereby 
assumed. 
This bold, at all events extraordinary method of observation led 
in a few months to the results published in the communications of 
