Physiology. — “On the Influence of the Season on Laboratory 
Animals”. By Prof. H. ZWAARDEMAKER. 
(Communicated at the meeting of January 29, 1921). 
This technical subject appears to be of general application. In 
previous publications the present writer and his co-workers have 
superadded to J. Lons’s balancing of ions of the circulating fluids, 
Na+ K 
—- = constant, the balancing for- 
Mg + Ca 
expressed in the equation 
Rt NO el 
mula = constant. Im the latter formula the radio- 
Ca + Sr + Ba 
physiological antagonism between K and (UO), + 7h. need not be 
taken into account *). 
Moreover, in earlier discourses the replacement of potassium by 
the other radio-active elements Rd, (U O),, U, Th, lo, Ra, Em, has 
been repeatedly discussed *). 
Now the present writer wishes to point out that the dosages in 
which these elements are to be administered must be much smaller 
in summer than in winter. Of course, this difference is not brought 
about by the radio-active elements as such, but by the fact that in 
summer the organs are more sensitized by certain substances *). 
These substances can be washed out, so that in the transition 
periods the functionating of a summer-organ during some hours’ 
perfusion with an artificial but nonetheless efficient circulating fluid, 
suffices to transform a summer-organ into a winter-organ. 
As regards sensitizing power, that of the washed-out substances 
is analogous to that of adrenalin. 
The organs operated upon were the hearts of frogs and of eels. 
A detailed publication will appear elsewhere. 
1) G. R. des Séances de la Soc. de Biologie 7 Juin 1919. 
2) Journal of Physiology Vol. 53 p. 273 1920. 
3) Proceedings of this Acad. 25 Sept. 1920. 
