oni i $, 
Ott, 2, 187 
3] 
NATURE | 465 
markedly tricrotic pulses, say from the femoral and also from the 
dorsalis pedis arteries. According to the view of Dr. Burdon 
Sanderson 2nd most other writers, the interval between the 
rimary and tidal wayes ought to be more than doubled in the 
orsalis pedis; according to the view of Mr. Garrod, on the 
contrary, that between the tidal and dicrotic waves. It will be 
found that there is no such considerable and constant variation 
as would be required by either theory, although the tidal wave 
aps not maintain its relative position so closely as does the 
icrotic wave. The kind of pulse best of all suited for this ex- 
periment is fortunately * rather’scarce ; it is that of a young 
person who has a granular kidney, but is free from dropsy, 
The theory of Mr. Garrod may appear at first sight suitable 
to one of the forms of healthy pulse, in which the tidal wave ap- 
pears as a slight elevation preceding the dicrotic wave ; but I do 
not think that it will be accepted by anyone who has watched its 
variation in a Jarge number of diseased pulses, and has seen it 
pass through eyery gradation, from a separate and distinct wave 
to a mere convexity in the descending curve, which may com- 
mence immediately from the top of the primary upstroke. In 
the pulse of rigid arteries this latter form is often taken when 
‘the heart is quiet, but when it acts more vigorously the tidal 
waye becomes separated, owing to the development of the so- 
called “percussion element,” which is really the effect of 2c- 
quired yelocity in the sphygmograph. The case which should 
afford the most crucial test is perhaps that very rare one in which 
the aortic orifice is closely obstructed, and scarcely any valves 
remain to produce a wave by their closure. The tidal wave 
should then, according to Mr. Garrod's theory, be at least greatly 
diminished, but, in point of fact, it is then more greatly deye- 
loped than under any other circumstances whatever. Evidence 
to the same effect may be derived from the use of an artificial 
heart with experimental elastic tubes, for it is found that, under 
suitable conditions, the tidal wave may be greatly prolonged by 
a protracted contraction of the heart. This was first shown by 
Mr. Mahomed in the Jedical Zines, and although I believe his 
theory to be erroneous as to the relation between the primary 
_and tidal waves, yet, with regard to the practical associations of 
the tidal wave, my experiments have led me to conclusions 
which are quite in agreement with his, namely, that three things 
contribute to the development of the tidal waye—increase of 
pressure, diminution of elasticity, and prolongation of the heart’s 
contraction. 
Mr. Garrod argues that the tidal wave cannot haye anything 
to do with the inertia of the long lever, because it is shown in 
the reflecting sphygmoscope, in which that is absent, I do not, 
however, consider that the result is due solely, and possibly not 
even chiefly, to the inertia of the lever, but to that of the instru- 
ment altogether, and inertia is possessed likewise by the sphyg- 
moscope. Moreover, since the latter dogs not record its indica- 
tions, it would be difficult to ascertain whether the tidal wave 
shown by it corresponds precisely to that of the sphygmographic 
tracing, Another instrument has also been called a sphygmo- 
scope, in which the motion of the pulse is shown by the variation 
ofa gas flame. In this there appears indeed the counterpart of 
the tidal wave, but not in the form of a single wave ; instead of 
this a series of small waves is shown. ~ These may appear only 
as a slight quivering motion, and are evidently due to the oscil- 
lation of the elastic diaphragm upon which the pressure of the 
pulse is received. 
Mr. Garrod maintains his own theory especially on the ground 
of observations with his cardio-sphygmograph, showing the 
commencement of the tidal wave in the radial pulse .to be syn- 
chronous with the closure of the aortic valves. But the deter- 
‘mination of the moment of that closure depends on the correctness 
of his interpretation of the minor elevations in the cardiographic 
tracing. ‘These are numerous, and his interpretation of them all 
is most ingenious, but to accept it requires an implicit faith that 
the instrument itself has no part in producing. any of the minor 
features of the curve. Now, that curve was drawn by a lever, 
moving ona pivot, and balanced between two springs, which 
would seem a contrivance peculiarly liable to oscillate. When 
therefore it is further found that in cardiac tracings published by 
other observers, or those obtained by applying the sphygmo- 
graph directly to the heart, there is no close correspondence 
either in the number or the position of the elevations, the con- 
clusion can hardly be resisted that some of them are due to such 
oscillation. My own opinion is that neither in the cardiographic 
* [We have omitted the prefix z= from this word; we hope Mr. Galabin 
will forgive us,—Ep.] 
2 
mal 2 g 
nor in the radial pulse tracing can the point corresponding to the 
end of’systole be precisely determined. 
The whole subject is one which it is difficult even to state in- 
telligibly without a constant reference to diagrams of tracings, 
and therefore, for a fuller account of my views as ta the theory 
of the pulse, particularly in reference to the complete explanation 
of the dicrotic waye, I must refer to a paper to be published in 
the next number of the Yournal of Anatomy and Physiology. 
While I consider that the construction of the sphygmograph 
has some influence on the tracing produced, yet I believe that, 
by a fortunate chance, the result is more practically useful than 
if the pulse-wave were recorded with perfect accuracy, for I think 
that slight differences in it, which would then perhaps escape 
notice, are, as it were, magnified and made manifest to the eye. 
I may say in conclusion that I do not quite agree in the view 
that we must wait for the practical application of the sphygmo- 
graph until physiologists are agreed about the theory of the pulse, 
for, according to present appearances, that consummation is 
distant indeed. There is, however, among sphygmographers an 
agreement about practical inferences which is almost as notable 
as the confusion which prevails as to mechanical causes, It is 
possible therefore for a person to use the sphygmograph for 
diagnosis and prognosis, who does not even attempt to under- 
stand the cause of the waves seen in its tracings. But it must 
be allowed that the settling of the mechanical question is much 
to be desired, and that, without it, the sphygmograph cannot 
afford that service, which otherwise it would he capable of doing, 
to the solving of all general physiological problems relating to 
the vascular system. And, from a practical point of view, these 
may perhaps be regarded as among the most important in phy- 
siology, for it is probably through the agency of the vascular 
system that many of the greatest effects of remedies are pro- 
duced. A. L. GALABIN 
On the Origin of Nerve-Force 
In a paper on this subject, by Mr. A. H. Garrod, in 
NATURE, vol. viii. p. 265, the author states that in cold-blooded 
animals, nerve-force must be generated by the difference between 
their own temperatures and that of the medium by which they 
are surrounded, Now, to take the case of a frog as a common 
example of a ‘‘so-called” cold-blooded animal: A few days 
ago, when the thermometer was standing at 71°, I took the tem- 
perature of two frogs, one was 69°, and the other 67°; the 
difference between their temperature and that of the surround. 
ing air was practically #7/, Now, on a day of this sort of tem- 
perature, it would seem that the pervious integument of the frog 
is continually exhaling moisture, and that in consequence the 
temperature falls, and would continue to fall below that of the 
surrounding air, were it not that it was raised by the heat gene- 
rated ‘* by the destruction of tissue that is continually going on 
within the body of the animal ;” so between these two contend- 
ing forces a state of equilibrium results, and the temperature of 
the animal and the surrounding air are the same. But, if this 
be true, it follows that the whole of the heat from the animal is 
used up in keeping up its temperature, and therefore none can be 
spared for conversion into nerve-force. Therefore, a frog at rest 
ona summer's day ought to have no nervous energy. Now, 
suppose our frog takes to leaping vigorously, he will develop a 
certain amount of heat, and then he ought to have a great deal 
‘of nerve-force ; but it is not found that an active frog is more 
“*nervous” than a quiescent one, 
Again, the neryous irritability of a frog, though perhaps not 
acting with the instantaneous energy with which it acts in a 
mammal, still persists far longer than in other vertebrates, and 
will continue much longer after the somatic death of the animal, 
when it is quite clear that the temperature of the body and the sur- 
rounding medium will be the same, Nowin this case the nerves 
may be so irritated as to lose all irritability, and yet, after a 
period of rest, this irritability will be regained, clearly, to my 
mind, showing that nervous energy must be generated after the 
death of the animal, when all differences of temperature have 
ceased, 
Finally, it must be admitted, without the aid of any hypothes 
sis, that the difference between the temperature of a frog and the 
surrounding air is, at any time, very slight ; and yet this animal 
possesses what we call an extremely “persistent” form of nerves 
force, 
R, LYDEKKER 
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