230 
THOMPSON YATES LABORATORIES REPORT 
In this case, as in all cases examined, certain irregularities will be noticed, show- 
ing a departure from the ideal case depicted by Du Bois Reymond's laws. It is 
convenient to assume that such irregularities are produced by accessory cross sections ; 
it is is not however believed that all, nor even the most important, irregularities are 
the outcome of such an accidental cause. It will be seen that experiments made upon 
carefully prepared and treated vagus nerves are not free from irregularities of an 
exactly similar kind, and in this connexion attention is drawn to the facts of Experi- 
ment (Tap Water, fig. W, see p. 279), in which the irregularities are demonstrated 
in a very striking manner by the use of a special expedient. 
In this section the important details of experiments are given which may serve 
to demonstrate the conditions actually to be met with. No attempt is made to 
arrange them with reference to any hypothetical simplicity, it being considered that 
the examination of actual curves, experimentally obtained, is of greater value. It is 
necessary to exhibit the phenomenon in some detail, because such a demonstration of 
actual measurements has never been previously undertaken, and because great pains 
have been taken to correct the observations made from the consequences of an 
unavoidable source of error most frequently neglected. 
This source of error is due to the alteration in the phenomenon taking place 
with lapse of time, but fortunately taking place, as will subsequently be seen, in a 
regular and definite manner. The change with lapse of time is not greater in 
mammalian nerve than in frogs ; it is, however, in either case considerable, and as 
the data of the experiment given below show, the error, unless corrected, is always 
vitiating the conclusions drawn from observations. Comparisons between differences 
of potentials found between sets of points, such as are made when an attempt is made 
to study the distribution of potential, are valueless, unless the routine method of 
conduction of the experiment permits the comparison to be made between corrected 
values inferred to exist at the same moment of time. 
EXPERIMENT A 
Vagus Nerve of Cat 
Piece of Nerve 6 centimetres long 
The nerve was laid upon a dry ebonite scale forming a platform in the moist chamber. One non- 
polarizable electrode was placed in contact with a cross section and retained there throughout the 
experiment ; the other non-polarizable electrode was first placed in contact with a point distant I centi- 
metre from this, then upon a second point distant 2 centimetres, a third at 4. centimetres, a fourth at 
5 centimetres distance, an observation being taken in each case of the potential difference between each 
point and the cross section. The experiment was continued by a return of the second electrode to 
point (4.), then to point (3), then to point (2), then to point (1). Thus two observations were taken at 
each point, once going up and once going down the nerve, and a definite interval of time was allowed for 
each observation. 
