914 
secondary chemoreceptors, there must also be substances present in 
the serum, that intensify the action of poisons like pilocarpin on the 
surviving catgut (of course it is possible that these two substances are the 
same). We considered it of great importance to ascertain whether 
this phenomenon was an isolated instance or one out of many. In 
order to make this out we first of all ascertained whether, besides 
serum, there are other substances that exert a similar intensifying 
influence on pilocarpin and on other poisons, and secondly we did 
not confine ourselves to the study of the influence of poisons on 
surviving organs, but we have also examined the influence on the 
intact animal. In this first communication we will report only the 
results of our investigations of the surviving gut. 
Influence of rabbit's serum on the sensitivity of cat-guts to 
pilocarpin. 
In this set we experimented on the surviving cat-gut and always 
took — as in previous researches — strips of the small intestine 
of a cat, from which the mucosa had been removed. The intestine 
was opened along the place of insertion of the mesentery and after 
the mucosa had been removed a piece was cut off on either side 
of the place of insertion, so that only the contractions of the longi- 
tudinal fibres and not those of the circular fibres were registered. 
Guts treated in this way are peculiarly appropriate for a quantitative 
inquiry into the action of poisons. There is moreover the advantage 
that in the ice-box they keep good for days. 
The sensitivity of guts treated in this way varies considerably. 
Sometimes at the first administration they react on the small quan- 
tum of 0,01 mgrms of pilocarpin, but at other times much larger 
quanta, up to 1 mgr. are required. However, after washing out the 
first doses and adding again pilocarpin every time, the sensitivity of 
the gut will, in most cases, augment considerably. We found that 
when this process of repeated washing and again administering the 
poison is prolonged sufficiently, the sensitivity of the gut will at 
length be such as to present a contraction with doses of about 
0.01 mgrms of pilocarpin added to 75 ccm of Tyrode. When this 
condition is arrived at, the successive equal doses of pilocarpin—washed 
out after three minutes every time — produce an equal effect, and 
only then did we administer serum to examine its influence upon 
the sensitivity of the gut. It is essential to call particular attention 
to this proceeding, for it stands to reason that in the initial stage 
of the experiment, when the gut reacts only on large doses of pilo- 
