Physiology. — “Zrperimental Influence on the Sensitivity of vari- 
ous animals and of Surviving Organs to Poisons’. 1st Part. By 
W. Storm VAN LEEUWEN and Miss C. van DEN BroukKe. (Com- 
municated by Prof. R. Maenvs.) 
(Communicated at the meeting of January 31, 1920). 
In a previous paper *) STORM VAN Leeuwen has shown that in the 
serum and in the tissues of various animals there are substances — 
called .by him free chemoreceptors — that are capable of adsorbing 
alkaloids. On the basis of these researches he came to the conclusion 
that the sensitivity of various animals to poisons — particularly 
alkaloids — does not depend only on the sensitivity of the organs 
acted upon by the poisons, but also on the number of “free chemo- 
receptors” *) present in the body. 
In these experiments he had repeatedly to ascertain the influence 
of pilocarpin and of mixtures of pilocarpin and serum on surviving 
cat-guts. Thereby it appeared that, as a rule, a dosis of pilocarpin 
administered after previous treatment of the gut with serum 
exerted a stronger influence than before this treatment. In the 
experiments reported in this paper we have studied this problem 
more systematically, and in so doing we have arrived at the con- 
clusion that this serum may have a twofold influence: when e.g. 
rabbits serum is mixed with pilogarpin, this combination will affect 
the surviving gut much less than pilocarpin alone would do, because 
rabbit's serum, as mentioned before, contains substances that adsorb 
pilocarpin; if, however, we add to the solution in which the gut is 
suspended, first pilocarpin, subsequently serum and finally, after washing 
out the serum, again pilocarpin, the second quantum of pilocarpin 
will exert a stronger influence than the first. It follows, therefore, 
that besides the substances that can adsorb alkaloids, i.e. free or 
') W. Storm vAN LEEUWEN. Sur l'existence dans le corps des animaux, 
de substances fixant les alcaloides. Arch. Néerland. de Physiologie T. II, p. 650. 1918. 
*) Afterwards we deemed it better to call these free chemoreceptors “secondary 
chemoreceptors” in contradistinction to “dominant chemoreceptors”. 
60* 
