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movable pith) was placed: 1. at the apex; 2. '/, cm. lower than the 
apex and 3. 1 cm. lower than the apex of the atrium. This took 
place both for the right and the left atrium, and also for the two 
atria combined. 
Fig. 2 (a, b, and c) shows how the amplitude of top P* from the 
atrio-electrogram diminishes in size as we descend with the electrode 
from the apex along the lateral side of the right atrium. The greatest 
potential difference, therefore, is manifest between basis and point, 
whilst each point of the atrium, lying lower than the apex, at deri¬ 
vation offers a smaller potential difference with the sinus. This is 
quite in accordance with the usual representation, at which it is 
supposed that, taking into consideration the fact that the contraction- 
stimulus arises from the sinus, the stimulus regularly goes on in 
the atrium tissue from the basis to the point of the atrium. 
In the same figure 2c may also be demonstrated the appearance 
of a small elevation, with following slight fall in the electrogram, 
manifesting itself a full second before the commencement of the myo¬ 
gram of the atria. 
This elevation may be attributed to the sinus, among others for 
this reason that this elevation in size increases according as we draw 
nearer to the sinus. 
Already in a former communication I have alleged grounds to 
prove the independence of the electrical phenomena of the heart with 
respect to the changes of form. In the atria of Einys this quality 
can be demonstrated very clearly. 
A part of the heart of Emys consisting of only atria and sinus is, 
isolated, brought into a gas-chamber, and derived in one place 
fcom the sinus, in another place from one of the two atrium-tops 
or from both tops at the same time. In this way different combina¬ 
tions of derivation may be brought about. The movements of the 
two atria are, by means of a simple suspension, registered by the 
silhouette of the little levers. If 2 cm 3 of chloroform are administered 
which are evaporating in the gas-chamber, the mechanic movements 
are gradually growing smaller, so that at last they stop entirely, 
II minutes after the administration the chloroform. Also at an examina¬ 
tion of the atria no trace of motion is to be observed, whilst however, 
the electric phenomena continue showing themselves periodically very 
clearly, through in shape they are a little more complicated than 
before the poisoning. In fig. 3a and fig. 3 b the electrograms have 
been denoted as they are obtained by derivation of the sinus with 
the one electrode and derivation of the two atria-tops with a double 
other electrode. After evaporation of the chloroform by opening 
