and garden parties. Special services to Bombay, there being some two thouwere held in the Episcopalian, Presby- sand deaths in the presidency. In 1897 terian and Roman Catholic churches, and the University of Dublin conferred honorary degrees on a number of the distinguished visitors. THE bulletin with this title prepared by Assistant Surgeon General, J. M. Eager, and issued by the Public Health and Marine Hospital Service, exhibits in a bald way the relentless forward march of the bubonic plague, a circum stance more terrible and dramatic perhaps than anything else in contemporary history. Emerging from the obscure endemic focus in the province of Yunnan, China, in the year 1894, the plague appeared in Canton, and there were a hundred thousand deaths between March and August. The disease spread to Hong Kong and in 1896 there were over 55,000 deaths in India, including nearly 10,000 in the city of Bombay, with sporadic cases in Japan and Turkey. In 1898 there were 117,000 deaths in India, and extending far from its endemic home, there were cases in Madagascar and Mauritius. In 1899 there were 135,000 deaths in India and serious epidemics in China. Cases occurred in Egypt and the Hawaiian Islands, and South America was invaded. There were local epidemics in Portugal and Russia. In 1900 there was a diminution in India, the deaths falling to 92,000, but the disease invaded San Francisco and was present, and remains present, in every quarter of the world, Europe, Asia, Africa, Oceanica, North and South America. In 1901 the hope of relief in India was disappointed, the deaths rising to 278,000, and in 1902 to 575,000. They increased further to 835,000 in 1903, and to the neighborhood of one million in 1904 and 1905, falling in 1906 to 332,000, but rising again last year to the appalling record of 1,400,000 cases and 1,200,000 deaths. The plague was present in all quarters of the world, there being 156 cases and 76 deaths in San Francisco, and cases in the suburbs and in Seattle. If it were not for the great advance of modern medicine western civilization would be threatened with a disaster unparalleled since the middle ages. But the means by which the plague is transmitted have been discovered-we can exterminate fleas and rats if necessary-and, thanks to the labors of scientific and medical men, not a few of whom have sacrificed their lives, we are comparatively secure. But protective measures and more knowledge are needed here and in many directions, and the governments of the world should spend not less care and money on them than on their armaments. SCIENTIFIC ITEMS WE record with regret the deaths of Dr. Charles Harrington, professor of hygiene in the Harvard Medical School and chairman of the Massachusetts State Board of Health; of the Earl of Rosse, F.R.S., who, like his father, made valuable contributions to astronomy; of M. E. Mascart, since 1871 director of the French Meteorological Office, and of General J. F. Nery Delgado, for many years director of the Geological Survey of Portugal. THE Academy of Sciences at Turin has awarded its Riberi prize of the value of $4,000 to Professor Bosio, of Turin, for his discoveries in relation to the biological reactions to arsenic, tellurium and selenium.-The British Ornithologists' Union will celebrate its fiftieth anniversary in December next, when gold medals will be presented to the four surviving original members: Dr. F. Du Cane Godman, F.R.S., Mr. P. S. Godman, Mr. W. H. Hudleston, F.R.S., and Dr. P. L. Sclater, F.R.S. PROFESSOR L. H. BAILEY has been given leave of absence from the direct orship of the College of Agriculture of THE Berlin Academy of Sciences has received a legacy of $7,500,000 from Herr Samson, a banker of that city. M. Henri Becquerel has bequeathed $20,000 to the Paris Academy of Sciences in memory of his grandfather and his father, who were members of the academy. THE POPULAR SCIENCE MONTHLY. DECEMBER, 1908 THE CAUSE OF PULSATION BY ALFRED GOLDSBOROUGH MAYER DIRECTOR OF THE DEPARTMENT OF MARINE BIOLOGY OF THE CARNEGIE INSTITUTION OF WASHINGTON THE HE following is an account of a research which was pursued at the Marine Laboratory of the Carnegie Institution at Tortugas, Florida. An interesting jellyfish, Cassiopea ramachana, lives upon the muddy bottoms of the lagoons of coral islands in the Florida and West Indian regions. Here the stilted roots of dense green mangroves fringe many a lagoon whose half stagnant waters have never felt the surge of ocean waves. Looking down through the clear depths one sees the bottom almost carpeted with the Cassiopea medusæ. Over wide areas they lie with their disks nearly touching and their bell-rims languidly pulsating. At a glance one might mistake them for sea-weeds, deceived as one would be by their delicate blue-green and gray-blue color, and by the tree-like shape of the branching appendages which bear the mouths of the medusa, and which project upward and outward hiding the pulsating disk below them. At regular intervals around the rim of the jellyfish we find about sixteen minute club-shaped organs, each set within a deep niche. The microscope serves to show us that each of these little clubs contains at its outer end a mass of crystals, and upon one side a simple cup-like eye. Even in medusa six inches in diameter these sense-clubs are smaller than the heads of the smallest pins; mere specks barely discernible to the eye, yet if they be cut off we find that the medusa ceases to pulsate, while the cut-off portion of the rim still contracts rhythmically. It is thus evident that the stimulus which produces each and every pulsation arises in the sense-clubs. The question is, why is it that the central disk of the medusa does not pulsate in sea-water when its sense-clubs are removed? Curiously enough, if we stimulate the disk in any manner, such as by a mechanical or electrical shock, or by touching it with a crystal of common salt, it gives a few vigorous pulsations and then lapses into quiescence. But if we cut out the center of the medusa and also remove the rim, thus forming a ring tissue without sense-organs (Fig. 2), this FIG. 1. LIVING MEDUSE OF Cassiopea xamachana ON A SANDY BOTTOM. The large medusa in the middle is in the natural attitude with its mouth-arms uppermost. The smaller medusæ have been turned over in order to show their pulsating disks. ring remains quiescent in sea-water unless we stimulate it at any point such as at S with a single momentary touch of a crystal of potassium, or in some other manner, when a contraction-wave starts out from the point touched. In a narrow ring, however, the waves can go only in opposite directions from the stimulated point. Now one of these waves is apt to be strong and the other weak; for the nervous network which C FIG. 2. SHOWING HOW A PULSATION-WAVE MAY BE ENTRAPPED IN A transmits them is almost certain to be more complete on one side than on the other of any stimulated point. Of course the waves meet as in Fig. 2, B, and then the strong wave destroys the weak one and continues around the ring. There is then only one wave left in the circuit and this travels constantly around (Fig. 2, C) for hours or days until something stops it, such as the cutting of the circuit or a fresh stimulus which produces a wave that meets and destroys it. The weak wave was destroyed by the strong one in the above experiment because a weak stimulus can not set tissue into pulsation, which has been caused to pulsate through a strong stimulus, until after an appreciable interval of rest. Thus a weak stimulus following immediately after a strong one will produce no contraction, whereas a strong stimulus may cause tissue to pulsate even immediately after it has responded to a weak one. It is now evident that the disk without its sense-organs can pulsate in sea-water if only a wave be once started in it, but that under normal conditions there is nothing to start a wave, and thus the disk remains quiescent. In other words, the sea-water is indifferent, and neither stimulates nor inhibits pulsation. It is now time for us to determine why it is that the sea-water does not stimulate the disk when its sense-organs are removed. In the first place we must know the composition of sea-water, and chemical analysis shows that it consists of a mixture of sodium chloride (common salt). magnesium chloride and sulphate, potassium chloride, and calcium. chloride and sulphate. Numerous experiments show us that the common salt is a strong stimulant to both nerves and muscles. On the other hand, magnesium, calcium and potassium, all inhibit and do not stimulate the disk. Indeed, the stimulating effect of the common salt in the sea-water is exactly offset by the subduing tendency of the magnesium, calcium and potassium; and thus it is that the sea-water as a whole neither stimulates nor inhibits the pulsation of the jellyfish. The sea-water main |