When vagus stimulation does not cause complete standstill, but only a marked slowing, the strength of the slow ventricular beats is usually much less than the normal.

The reduction in contraction force does not bear any constant relation to the degree of slowing. While all the slow beats are weakened in some degree, a beat occurring after a long pause is sometimes decidedly stronger than one occurring after a shorter pause; on the other hand, the converse more often holds good-a beat occurring after a long pause is weaker than a beat occurring after a shorter pause.

The depression of contraction force does not appear to depend on over-distension of the ventricles during the slowing or standstill; nor upon the fall of arterial pressure that occurs and involves a diminished resistance to the ventricular systole and a change in the coronary circulation.

The force-depressing effects of vagus stimulation can still be seen (1) when the superior and inferior vena cava have been clamped; or (2) when the pulmonary artery or (3) the aorta has been clamped; or (4) when all these vessels have been clamped before the vagus stimulation.

2. When slowing or arrest of the ventricular action occurs as a result of vagus stimulation, there is a marked change in the shape and duration of the ventricular curves; the degree of change stands in close relation to the length of the pause preceding each beat. The curves become broader near the top, and their duration is increased. The longer the interval preceding a curve the broader the curve is, and the more markedly is it prolonged. These features are not abolished when the superior and inferior vena cava have been clamped before the vagus stimulation; nor when the aorta or the pulmonary artery, or all these vessels, have been clamped.

3. The vagus appears to inhibit the spontaneous rhythmic tendency inherent in the ventricles; the ventricular standstill does not appear to be due simply to the standstill of the rest of the heart.

4. At the same time the absence of auricular beats of any considerable strength is usually a necessary condition for the occurrence of a protracted ventricular standstill. It commonly but not invariably happens that if the auricles are artificially excited to contract during the period of cardiac standstill, the ventricles beat also in sequence to the artificially excited auricular contraction.

5. When the heart begins to beat after a period of inhibition, the order of contraction most commonly seen is that which obtains normally ostial parts of the great veins; auricles; ventricles. But sometimes the ventricles recommence, and give one or more beats before any contraction occurs in the other parts of the heart.

6. There are sometimes seen evidences of the occurrence under vagus influence of a block in the propagation of the contraction from

auricles to ventricles. At certain phases of vagus stimulation the ventricles often fail to respond to auricular beats, while at the same time there is evidence to show that this is due not to a depression of the ventricular excitability, but to a break in the transmission of the contraction from the auricles.

7. The maximum intensity of the inhibitory influence exerted by vagus stimulation often obtains at the same time in the auricles and the ventricles. But frequently the auricles become greatly depressed, while the ventricular beats are of undiminished size, or are only beginning to be affected; in rare cases the ventricular contraction force becomes reduced more suddenly than the auricular.

8. The effects of vagus stimulation on the ventricles may be in some measure counteracted by the application to the ventricular surface of a series of stimulations (e.g., single induction shocks) at about the normal rate of the heart's action. An artificially excited series of beats is thus caused; these beats give curves of approximately normal form and duration, and they are much stronger than any slowly occurring spontaneous beats that appear after the standstill has lasted for some time; they are also much stronger than single beats excited (by induction shocks) at long intervals during the standstill. The beats of the artificially excited series (at normal rate) are still decidedly weaker than normal beats.

On the Existence of a Local "Inhibitory Area" in the Heart.

By stimulation of a certain locality on the dorsal aspect of the auricular surface, certain striking effects are obtained. In the cat and dog the area in question is elongated in shape, and is situated over the inter-auricular septum, its long axis running parallel with the plane of the septum. It extends downwards to within a short distance of the coronary sinus. At the right side of the area lies the termination of the vena cava inferior.

Many nerves course downwards through this region; there are also numerous nerve-cells and ganglia. These, however, are not confined to the area in question, but occur in considerable number over the dorsal aspect of the left ventricle, especially in its septal half. The nerves appear to be derived to a considerable extent from the left vagus. The majority of the fibres are non-medullated, but medullated fibres are also present (cat). Ganglia occur in special abundance near the auriculo-ventricular groove.

Stimulation of this area with an interrupted current gives results that stand out in sharp contrast to those obtained by stimulating other parts of the auricular wall, e.g., the appendix. Stimulation of the latter causes an acceleration of both auricles and ventricles. The auricles contract with great rapidity, so that they present a peculiar

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fluttering appearance; the ventricles beat much more rapidly than before, though they do not keep pace with the auricles.

On the other hand, stimulation of the inhibitory area, while it causes a rapid fluttering action of the auricles, induces either a very marked slowing, or a complete standstill in the ventricles. This result is a mixed one-ventricular inhibition, resulting from stimulation of certain structures in the inhibitory area, and auricular acceleration, in all probability due to an escape of the stimulating current to the excitable auricular tissue.

The inhibitory effects on the ventricle much resemble those caused by vagus stimulation. There is depression of the ventricular contraction force, and changes in the shape and duration of the ventricular curves similar to those occurring under vagus influence. Stimulation of the inhibitory area and of the vagus are both rendered ineffective by the administration of atropine.

But there are certain points of difference :

(1.) The strength of current necessary to inhibit the ventricles is very much less when the current is applied to the inhibitory area than when it is applied to the vagus.

(2.) Stimulation of the inhibitory area remains effective in arresting the ventricular action, after curare has been administered in such amount as to cause stimulation of one or both vagi in the neck to be entirely without inhibitory result.

(3.) In many instances when the vagi have become exhausted, or have lost their inhibitory power from less definite causes, the inhibitory area remains effective.

It seems clear from the very different relation borne by the inhibitory area to certain poisons, to the strength of stimulating current necessary, to exhaustion, &c., that in exciting this area we are dealing with structures of a more or less special nature, differing markedly in their character from the ordinary inhibitory fibres running in the trunks of the vagus nerves.

The important structures of the inhibitory area are situated superficially; they may be readily paralysed by the application of a few drops of a 4 per cent. solution of cocaine hydrochlorate, or of strong ammonia.

The region in question does not contain a motor centre for the heart muscle. Destruction of this area does not arrest the spontaneous rhythm of the organ (which indeed originates in parts some distance removed from the inhibitory area, viz., in the ostial parts of the great veins, especially the vena cava superior and the pulmonary veins). Nor is the propagation of the contraction from one part of the heart to another in any way deranged or interfered with.

The inhibitory area probably contains structures to which many at

least of the inhibitory fibres of the vagus go, there to come into intimate relation with the cardiac mechanism.

Effect of Stimulation of Ostial Parts of Great Veins in certain Abnormal Conditions.

At certain stages of the process of asphyxia, and in the dying heart, there is often seen a very remarkable alteration in the behaviour of the ostial parts of the great veins towards direct stimulation with interrupted currents. In such circumstances, an inhibition of the spontaneous rhythmic action of these parts may often be seen as a result of direct stimulation, whereas in the normal state such a stimulation is productive of immediate and striking acceleration.

VI. "On the Structure of the Electric Organ of Raia circularis." By J. C. EWART, M.D., Regius Professor of Natural History, University of Edinburgh. Communicated by Professor J. BURDON SANDERSON, F.R.S. Received April 30, 1888.

(Abstract.)

This paper gives an account of the structure of the cup-shaped bodies, which, as mentioned in a previous paper read 26th April, 1888, make up the electric organs of certain members of the skate family. The structure of these electric cups has been already studied in three species of skate, viz.: Raia fullonia, R. radiata, and R. circularis. The present paper only deals with the electric organ of R. circularis. It shows that the cups in this species are large, well-defined bodies, each resembling somewhat the cup of the familiar "cup and ball." The cup proper, like the disks of R. batis, consists of three distinct layers, (1) the lining, which is almost identical with the electric plate of R. batis; (2) a thick median striated layer; and (3) an outer or cortical layer. The lining or electric plate is inseparably connected with the terminal branches. of the numerous nerve-fibres, which, entering by the wide mouth in front, all but fill the entire cavity of the cup, and ramify over its inner surface, the intervening spaces being occupied by gelatinous tissue. This electric layer, which is richly nucleated, presents nearly as large a surface for the terminations of the electric nerves as the electric plate which covers the disk in R. batis and R. clavata. The striated layer, as in R. batis, consists of numerous lamellæ, which have an extremely contorted appearance, but it differs from the corresponding layer in R. batis, in retaining a few corpuscles. The cortical layer very decidedly differs in appearance from the alveolar layer in R. batis. It is of considerable thickness, contains large nuclei,

and sometimes has short blunt processes projecting from its outer surface. These short processes apparently correspond to the long complex projections which in R. batis give rise to an irregular network, and they seem to indicate that the cortical layer of R. circularis essentially agrees with the alveolar layer of R. batis, differing chiefly in the amount of complexity. Surrounding the cortex there is a thin layer of gelatinous tissue in which capillaries ramify. This tissue evidently represents the thick gelatinous cushion which lies behind the disk in R. batis, and fills up the alveoli.

The stem of the cup is usually, if not always, longer than the diameter of the cup. It consists of a core of altered muscular substance, which is surrounded by a thick layer of nucleated protoplasm continuous with the cortical layer of the cup, and apparently also identical with it.

The cups are arranged in oblique rows to form a long, slightly. flattened spindle, which occupies the posterior two-thirds of the tail, being in a skate measuring 27 inches from tip to tip, slightly over 8 inches in length, and nearly a quarter of an inch in width at the widest central portion, but only about 2 lines in thickness.

The posterior three-fifths of the organ lies immediately beneath the skin, and has in contact with its outer surface the nerve of the lateral line. The anterior two-fifths is surrounded by fibres of the outer caudal muscles. It is pointed out that while the organ in R. circularis is larger than in R. radiata, it is relatively very much smaller than the organ of R. batis.

VII. "On Æolotropic Elastic Solids." By C. CHREE, M.A., Fellow of King's College, Cambridge. Communicated by Professor J. J. THOMSON, F.R.S. Received May 1, 1888.

(Abstract.)

This paper treats of elastic solids of various non-isotropic kinds. Its object is to obtain solutions of the internal equations in ascending integral powers of the variables, and apply them to problems of a practical kind, some of them already solved, but in an entirely different way, by Saint-Venant.

On the multi-constant theory of elasticity the equations connecting the strains and stresses contain 21 constants. As shown by SaintVenant these reduce for one-plane symmetry to 13, for three-plane symmetry to 9, and for symmetry round an axis perpendicular to a plane of symmetry to 5.

Part I of this paper deals with one-plane symmetry. A solution is obtained of the internal equations of equilibrium complete so far as