Page:Popular Science Monthly Volume 3.djvu/806

782 in endless succession. In order to admit of these changes, the auriculo-ventricular valves, as has been stated, rise and fall like the diaphragm in respiration; the valves protruding, now into the auricular cavities, now into the ventricular ones. There is in reality no pause in the heart's action. The one movement glides into the other as a snake glides into the grass. All that the eye can detect is a quickening of the gliding movements, at stated and very short intervals. A careful examination of the sounds of the heart shows that the sounds, like the movements, glide into each other. There is no actual cessation of sound when the heart is in action. There are periods when the sounds are very faint, and when only a sharp or an educated ear can detect them, and there are other periods when the sounds are so distinct that even a dull person must hear; but the sounds—and this is the point to be attended to—merge into each other by slow or sudden transitions. It would be more accurate, when speaking of the movements and sounds of the heart, to say they are only faintly indicated at one time, and strongly emphasized at another, but that neither ever altogether ceases. If, however, the heart is acting more or less vigorously as a whole, the question which naturally presents itself is, How is the heart rested? There can be little doubt it rests, as it acts, viz., in parts. The centripetal and centrifugal wave-movements pass through the sarcous elements of the different portions of the heart very much as the wind passes through the leaves: its particles are stirred in rapid succession, but never at exactly the same instant; the heart is moving as a whole, but its particles are only moving at regular and stated intervals; the periods of repose, there is every reason to believe, greatly exceeding the periods of activity. The nourishment, life, and movements of the heart are, in this sense, synonymous."

Poisoning by Oxygen.—M. Paul Bert, whose observations upon the physiological effects of high atmospheric pressure we have already noted in the Monthly, communicates to the Paris Academy of Sciences the results of his observations on the toxic action of oxygen. Placing sparrows in oxygen under a pressure of 350 (that of the atmosphere being represented as 100), he found the birds seized with violent convulsions. The same result followed when sparrows were confined in common air under a pressure of 11 atmospheres. In oxygen, at 3½ atmospheres' pressure, or in air at 22 atmospheres, the convulsions were extremely violent and quickly fatal. The symptoms in the latter case were these: Convulsions set in after four or five minutes: in moving about, the bird hobbles on its feet, as though walking on hot coals. It then flutters its wings, falls on its back, and spins about, the claws doubled up. Death supervenes after a few such spasms.

The toxic dose of oxygen for a dog was found to require, for convulsions, a pressure of 350 in oxygen; and a pressure of 500 is fatal. The amount of oxygen in the arterial blood of a dog in convulsions was found to be considerably less than twice the normal quantity. Hence the author's startling conclusion, that oxygen is the most fearful poison known.

Taking a dog in full convulsion out of the receiver, M. Bert found the paws rigid, the body bent backward in the shape of an arch, the eyes protruding, pupil dilated, jaws clinched. Soon there is relaxation, followed by another crisis, combining the symptoms of strychnine-poisoning and of lockjaw. The convulsionary periods, at first recurring every five or six minutes, become gradually less violent and less frequent.

The author sums up his conclusions as follows: 1. Oxygen behaves like a rapidly-fatal poison, when its amount in the arterial blood is about 35 cubic centimetres per cent, of the liquid; 2. The poisoning is characterized by convulsions which represent, according to the intensity of the symptoms, the various types of tetanus, epilepsy, poisoning by phrenic acid and strychnine, etc.; 3. These symptoms, which are allayed by chloroform, are due to an exaggeration of the excito-motor power of the spinal cord; 4. They are accompanied by a considerable and constant diminution of the internal temperature of the animal.

Infant Mortality.—During the year 1868, 23,198 children under one year of age, died by convulsions in England, the