1041 
stage. It is remarkable that this toxical stage can promptly be 
reduced again to the normal rhythm in which every systole of 
the auricle is followed by a powerful systole of the ventricle. 
In Fig. 14 we see a representation of the same frog’s heart of 
Fig. 13, but now after the sinus venosus has two minutes previously 
been refrigerated during a short time. After this refrigeration the 
rhythm of the ventricle became quite normal again, so that every 
systole of the auricle was followed by a systole of the ventricle. 
After the refrigeration the sinus venosus assumes gradually again 
the temperature of its surroundings, by which the tempo of the 
pulsations of the heart is quickened again. The consequence of this 
is, that the toxical stage shows again irregular curves of the ventricle. 
On the diastolic line the last but one curve of the figure shows a 
second large elevation, which proves that at that moment the conducti- 
bility in the ventricle is considerably disturbed. This deformed 
curve is, as always is tbe case, followed by a prolonged pause and 
a succeeding enlarged systole. From this moment the former irregu- 
larities in the curves of the ventricle appear again. This experiment 
is very instructive. If we ask why through this simple intervention 
we could make the toxical stage return to the therapeutic one, the 
answer to this question can easily be found. The irregularities 
described above were brought about by the circumstance that the 
refractory stage of the ventricle or of part of the ventricle lasted 
longer than 1 sinus-period. Consequently the ventricle or part of it 
was at a given moment not able to react upon the “Erregung” 
that reached it from the auricle. The refrigeration of the sinus 
venosus prolongs the duration of the periods of the heart, so that 
the wrong proportion does not exist any longer and the normal 
rhythm is restored. This affords us a new indication that the irre- 
gularities we have described are caused by a wrong proportion 
between the duration of the refractory stage and the duration of the 
sinus-periods. This experiment teaches us likewise that in the pharmacy 
of the digitalisgroup a dose is then toxical, when the frequency of 
the heart is a definite one. At high frequencies the toxical dose is 
much smaller than at low frequencies. This holds likewise for 
veratrine. 
3. Third stage. During the third stage the periods of Luciani 
occur. The auricles continue to pulsate during the pauses in the 
normal tempo, so that we have here to do with periods of the ventricle 
(consequently of the contracting extreme organ). The ascending-stairs 
in the beginning and the descending-stairs towards the end of a group 
