ON ELECTRICAL CHANGES. 601 
the direct effects produced by changes in the blood-vessels contained 
in it. 
For this purpose direct experiments of a similar kind were carried out 
upon large blood-vessels. An artery was ligatured and divided, the cen- 
tral end (towards the heart) dissected from its surroundings, raised in air, 
and connected with galvanometer in same manner as nerves had been 
connected. The stretching was found of importance, and the femoral 
artery first chosen was abandoned for the carotid, as free from branches 
and, therefore, from local injuries during dissection. 
In such a preparation current changes are found proportional to 
changes of blood pressure of a gross kind and with a marked latency. 
The relation between two is of same kind as that found in the peripheral 
end of vagus nerve, a rise of pressure causing a fall of current. Such 
current changes are not due to alterations in resistance of tissue to any 
current found there, as their nature remains unaffected by the compensa- 
tion or over-balancing of the demarcation current, retaining always the 
same direction whatever the direction of current traversing tissue may be. 
As to the real source of such changes no positive statement can be 
made. The most probable cause would seem to be an alteration in tonus 
of muscular coat secondary to the change of pressure within vessel. This 
is supported by the result of one experiment, in which an otherwise unin- 
jured carotid artery was separated from surrounding tissues by a thin 
sheet of indiarubber and a portion of its length connected with the 
galvanometer. The galvanometric curve bore at first no relation to the 
blood-pressure curve, but a relation was imperfectly introduced by injury 
to artery at electrode distal from heart. In other experiments attempts 
were also made to introduce electrodes into blood stream, but experiments 
were lost owing to coagulation of blood and the effects of pressure upon 
electrodes themselves. It is, however, felt that without further evidence 
an attempt to fix source of origin is futile. 
It was thought that the general research might be assisted by a study 
of such changes as might be obtained under similar conditions from largest 
combination of nerve and artery to be obtained in body. Experiments 
were performed, in which the vagus and carotid, having been divided and 
ligatured at same place, were lifted up without being separated from one 
another. The piece of tissue so formed was stretched to its normal length, 
and its distal end connected to galvanometer in usual way. 
From this preparation it was found possible to obtain, with unfailing 
regularity, a galvanometer curve having the most marked correspondence 
to simultaneous blood-pressure curve, a rise of pressure being accompanied 
by a negative variation of current. 
It is to be noticed that the demarcation current obtained from this 
tissue was exceedingly small, and that the variations in it were of a 
magnitude bearing an extremely large ratio to it; in fact the most suc- 
cessful comparisons were made in preparations in which the origina! current 
was practically nil. Itis also of note that the quantity of change ob- 
tained from this preparation in response to a change of blood pressure is 
greater than that obtainable from carotid artery alone, and much greater 
than that obtainable from vagus nerve alone. 
In the total result it seems possible that a contribution is due to 
artery, a portion to nerve, and that in this case the components have 
same direction ; for ligature of nerve near to trunk and as far as possible 
