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ever, often differs from that of the other vascular organs in this respect. For, if the circulation be arrested absolutely on the right side of the heart, then, the current of blood passing through the pulmonary artery being cut off, the lungs may be left not only free from congestion, but bloodless; while the other vascular organs are largely congested. In cases, on the other hand, where the obstruction has commenced on the left side of the heart, and the current of the blood has been cut off in its passage through the aorta, the lungs may be the chief seat of congestion ; the other vascular organs being, by contrast, moderately free of blood.

CAUSE AND CAUSATION OF CARDIAC APNEA. In considering the cause and causation of the symptoms known in their collected sense under the term cardiac apnæa, we turn in every case to some one or other of the morbid conditions of the heart or blood for a predisposing cause. These conditions may, as we have seen, be varied ; but they have all this great feature in common, that they imply a deficiency either in the propelling power of the heart or in the sustaining power of the blood.

One or other of these predisposing causes present, any additional cause may prove the excitant which shall have for its tendency the sudden development of the predisposing cause. Thus, in examples of degenerated heart, mental shock and anxiety, too long a deprivation of food, sudden exertion, passion, sudden fear, diarrhea, over-repletion-any one of

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these-may act as an excitant of the paroxysm. That these excitants differ widely the one from the other is true; but the difference involves no paradox, for a heart enfeebled may be stopped as readily by calling it into a sudden action which it is not prepared to meet, as by withdrawing from it that sustainment of which it is not able to lose a tithe.

But, perhaps, the most frequent of all exciting causes is profound sleep. In the early hours of the morning, when the influence of the sun has been longest from the earth, and when the physical forces have to a considerable extent relaxed under the effects of sleep; when, in simple terms, the action of the heart, even in the healthy man, is at its minimum of propelling power, then are those who are predisposed to cardiac apnoea most readily affected; then not unfrequently they die, perhaps without awaking, or not dying, they awake in the midst of a paroxysm, the chest fixed and the body more or less tetanic. For this same reason, in cases far advanced, the inability to sleep, owing to the recurrence of the paroxysm, becomes, as we have seen, one of the most characteristic manifestations of the affection.

From this it happens that even events, trifling when they occur in the organism of a sound man, may turn the scale fatally in one disposed to cardiac apnea. For instance, flatulency leading to distension of the stomach, produces in the healthy individual but a temporary inconvenience, a little pain and fulness in waking hours, and at most a disturbed dream or nightmare during sleep. But in a man with a heart disorganised, when the distended stomach presses on the diaphragm, and inspiratory movements are slightly impeded, and the lung-circulation embarrassed, the feeble heart encounters a struggle for which it has no resources, and an apneal paroxysm is the result. I believe, indeed, that flatulency, acting in the way suggested, is beyond all others the most frequent exciting cause of cardiac apnæa in cases of cardiac disorganisation; and although, from being a cause temporary in its nature and removable, it is not necessarily a fatal excitant, yet occasionally it is even fatal when the degeneration has reduced the cardiac power to its minimum.

There are again cases, as we have seen, in which cardiac apnea may occur without any predisposing organic change; but in these instances some poison has been introduced into the blood, and has acted so suddenly and powerfully that the predisposition is not requisite, the exciting cause being immediately brought into action with all-sufficient potency. Poisons which produce these effects act one and all on the same general plan ; that is to say, they arrest the action of the heart primarily through the blood. They include a large group of poisons : some of the alkaloids, as strychnine, brucine, and nicotina: the ammonias, the cyanides, and certain of the volatile poisons, such as nitrite of amyl and amylene.

Turning now to the consideration of the symptoms presented during an attack of acute cardiac apnea, we find them reducible, physiologically, to one leading state-spasm of the muscular system, with its attendant details of pain and reduction of temperature. The recent progress of physiological science has led us closely to a correct understanding of the reason why this spasm should occur. It has shown us that this spasmodic state need have no organic lesion of the nervous centres for its cause, but that it is a product of a derangement existing between blood and muscle. Let me explain this as tersely as I can.

For the sustainment of the perfect balance of the muscular force, three conditions are absolutely required. First, it is necessary that the muscle should have a full supply of blood. Secondly, it is requisite that the blood thus supplied should possess the power of giving to the muscular structure a permanent temperature, which must not vary materially from 989. Thirdly, it is essential that the nervous connection betwixt the muscle and nerve-centre be everywhere intact. We can prove these positions by a variety of experiments.

We lay bare the heart of an animal and keep up artificial respiration. If the experiment be neatly done, and the animal operated on be kept gently anæsthetised, the heart may be observed, if the pericardium be unopened, beating rhythmically and with sufficient power to sustain both the pulmonic and systemic circuits for a long period of time. We watch the animal thus placed, and we observe that so long as the circulation is steady there is no convulsion, no spasm. But we interfere with this steady circuit of blood; we compress the great aorta, for instance, at its origin, and cut off the supply of blood in this way from the systemic circulation; and the results are, first, tremulousness, then convulsion, and finally tonic spasm.

Or, in lieu of mechanically arresting the blood through the aorta, we check it on the venous side, by compressing the superior and inferior cavæ; and now we see the heart cease action and its left side close in permanent systole: upon this the muscles of the systemic circuit become rapidly convulsed, and, as the blood which they retained is applied, spasmodically contracted.

If again, instead of mechanically obstructing the flow of blood, we inject through the pericardium upon the heart a stream of water reduced in temperature nearly to freezing point, we observe the heart make a rigid contraction; whereupon, the central organ ceasing its play and the muscles generally losing their vascular supply, there follow general tremor, convulsion, and spasm.

Once more, we modify the operation by injecting into the heart, through the external jugular, some one of the poisons I have named-ammonia, tobacco, hydrocyanic acid, strychnine; and, as the poison finds its way into the coronary system, we see first in the heart disturbance of action, palpitation, spasmodic contraction, cessation of motion, and afterwards a continuance of these changes carried on to the muscular system at large.

We may vary these experiments in a variety of ways. Instead of laying bare the heart, we may stop

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