Popular Science Monthly/Volume 43/May 1893/Popular Miscellany
Number of Glacial Periods.—An article by Prof. George F. Wright, in the American Journal of Science, is devoted chiefly to showing that certain points of evidence relied upon by those who believe that the "Glacial epoch" consisted of two periods of glaciation of similar extent separated by a long interglacial epoch, are insufficient to afford a basis for such a conclusion. Furthermore, the author adds to this: "As bearing against the duality of the Glacial period, it may be urged with great force that it is improbable that two periods should so nearly duplicate one another as these two are supposed to have done. To those who maintain the sufficiency of Croll's astronomical cause, however, this is rather an argument in favor. But, on the other hand, that cause would also demand a long succession of periods during all the geological ages, and of these we lack sufficient proof; while it would throw the two periods which Prof. Chamberlin recognizes back much farther than the facts will admit. It must be said, however, that it is not wholly out of analogy with known earth movements to suppose that there has been in connection with the Glacial period a succession of oscillations of the earth's crust nearly duplicating one another. Such oscillations seem to have occurred in various geological ages, as, for instance, during the coal period, when the successive coal beds were formed. And, indeed, much can be said in favor of the view that such an oscillation when once begun would perpetuate itself. . . . But our knowledge of these matters is too vague to reason of it with any confidence, as is that also of the other causes which have been suggested for the production of the phenomena of the period. In conclusion, it is sufficient to remark that our present state of knowledge on the subject seems so imperfect that it is not conducive to success in investigation to hold any theory as to the unity or duality of the period with great positiveness. Overconfidence on this point at the present time is likely to blind the eyes of the investigator, and to hinder progress both in the collection and in the interpretation of the multitudinous and complicated facts which everywhere invite our close attention."
Preservation of Leaves as Fossils.—In a paper on the Preservation of Plants as Fossils, Mr. Joseph F. James, of Cincinnati, names as one of the requisites to secure the preservation of any plant, that it must be in a position to be almost immediately covered by some material. A leaf or branch falling to the ground and likely to be exposed to the elements has a poor prospect of being preserved. But if it fall into the water and, sinking to the bottom of a lake or swamp or morass, be covered by mud or sand; or if it lie on the seashore and be covered by sand brought in with the tide, it may at least leave its mark. Or it may, through certain chemical properties it possesses, so act upon the stone on which it lies as to be preserved, not in actual substance, but as an intaglio. The author was impressed with the possibilities of the last process while walking along the street in the rain and looking at the fallen leaves on the pavements. He first noticed numerous irregular, discolored patches on the stone slabs. Looking more closely, he Bays: "I found that these discolorations had been caused by the leaves, which had left their impress on the stone. In many cases this impression was so distinct that there was no difficulty in recognizing the species. The leaves were those of the soft maple, one or two species of oak, tulip tree, and sycamore. There is here a possibility of the preservation of the remains of plants, or, at all events, of their impress upon stone, had it occurred under more favorable circumstances. But on a pavement, where people were passing constantly, the impressions were worn off and soon disappeared. The rain, however, did not seem to wash them away, so they were something more than mere surface markings." A similar phenomenon was observed and described in 1858 by Mr. Charles Peach in a paper on the Nature Printing of Sea-weeds, on the rocks of one of the Orkney Islands in Scotland.
Breath Figures.—Some interesting experiments are described by W. B. Croft in the production of "breath figures"—or latent impressions on contact of objects with glass and electrifying, which are made visible by breathing upon them. While there appears to be no limit to the durability of these figures if they are carefully protected, they usually become obscured by dust gathering on them after being often breathed upon. But certain changes or developments take place after the lapse of some weeks or months. In coin pictures, the object is near to the glass, but not in contact with it; for in the best specimens the rim of the coin keeps the inner part clear of the surface. Even if a coin only rest for a while on glass, an outline of the disk and sometimes faint traces of the inner detail will be produced when the spot is breathed upon. An examination paper, printed on one side, put between two plates of glass and left for ten hours, either in the dark or the daylight, will leave a perfect breath impression of the print, both on the glass that lay against the print, and on that which faced the blank side of the paper. Sometimes both impressions are white, and sometimes they are both black; or one may be part white and part black, or may even change while being examined. The impressions were very easy to produce during a sharp frost with east winds early in March, 1890. The following experiments easily succeed at any time: Stars and crosses of paper are placed for a few hours beneath a plate of glass; clear white breath figures of the device will appear. A piece of paper is folded several times each way to form small squares, then spread out and placed under glass; the raised lines of the folds produce white breath traces, and in one instance a letter-weight that was above left a latent mark of its circular rim. Some writing made on paper with ordinary ink and well dried, left a very lasting white breath image after a few hours' contact. Plates of glass lying for a few hours on a table cover worked with silk acquired strong white figures from the silk. Two cases have been reported where blinds with embossed letters left a latent image on the window near which they lay; it was revealed in misty weather, and had not been removed by washing. A glass which has lain above a picture for several years, but has been kept from contact by the mount, will often show on its inner side an outline of the picture, always visible without breath. The words white and black in the descriptions of the impressions relate to the adherence of the breath to the reliefs (white) or its non-adherence (black). The exact cause of the phenomenon is not known, but is supposed to lie in some of the unknown regions of molecular agency.
Exclusive Communities.—The number of ants dwelling together in a community, according to Sir John Lubbock, is sometimes as great as five hundred thousand. They are always friendly toward each other, no quarrel ever having been observed between two ants, members of the same community. They are, however, very exclusive, and regard an immigrant with horror. When an ant of the same species belonging to another nest appears among them, he is promptly taken by the leg or antenna and put out. It would naturally be surmised that this distinction was made by means of some communication. To test whether they could recognize each other without signs, attempts were made to render them insensible, first by chloroform and afterward by whisky. "None of the ants would voluntarily degrade themselves by getting drunk." Finally, fifty ants were taken, twenty-five from one community and twenty-five from another, and dipped into whisky until intoxicated. They were then appropriately marked with a spot of paint and placed on a table where the ants from one nest were feeding. The sober ones noticed the drunkards and seemed much perplexed. At length they took the interlopers to the edge of the moat surrounding the table and dropped each one into the water. Their comrades, however, they carried home and placed in the nest, where they slept off the effects of the liquor.
The Comma Bacillns, Cholera, and Sanitation.—Experiments by Prof, von Pettenkofer and Prof. Emmerich, in which they swallowed fresh cultures of comma bacillus upon empty, neutralized stomachs, show conclusively to von Pettenkofer that the comma bacillus, during its sojourn in the intestine, does not produce the specific poison that causes Asiatic cholera. This agrees with the results obtained by Bouchard, who was able to induce the symptoms of cholera in rabbits by giving them the excreta of human cholera patients, but not by giving them pure cultures of comma bacilli or their metabolic products. While he does not deny that the comma bacillus has some etiological importance, von Pettenkofer can not believe it is the x which, without the assistance of y, can cause epidemics of cholera; and he reiterates his wellknown views on the influence of the soil, especially in connection with the rainfall. His practical teaching may be summarized in the formula that it is the y—that is, the local physical and sanitary conditions—that must be attended to; each place must, in short, be made cholera-proof by sanitation.
Children and Flowers.—In a paper read before the Society of American Florists, on training children to love and cultivate flowers, Mr. Robert Farquhar argued that we could either stifle or strengthen the love of Nature which is planted in every young heart. If we encourage and cultivate this love the mind of the growing child will be opened to the beauties of Nature, and we shall in this way provide for it a means of healthy exercise out of doors and a source of delightful recreation all through life. Children should have gardens of their own to care for, and they should be instructed in garden practice. They should be allowed to sow the seed and care for the plants themselves, although they should be directed in all these operations. Florists who do business in villages and towns enjoy opportunities for doing effective work among children by explaining to their young visitors the methods of propagation. The claims of children should never be forgotten in making up the lists of premiums for agricultural and horticultural fairs. Prizes should be given for plants grown by them and for bouquets and collections of wild flowers made by them. Village improvement societies are doing excellent work in many sections. Some have distributed seeds and plants to the school children with most satisfactory results.
African Pluck.—Mr. Alfred Coode Hore, in his Eleven Years in Central Africa, speaks well of the tribes of the Tanganyika region, which he finds are peaceable and industrious for the most part, but turbulent and aggressive when they have learned to dread molestation by strangers. "It seems hard," he says, "that a man should be called lazy because he has ample leisure between his busy times; who has made with his own hands from Nature's raw materials his house, his axe, hoe, and spear, his clothing and ornaments, his furniture and corn-mill, and all that he has, and who, though liable often in a lifetime to have to commence that whole process over again, has the energy and enterprise to do so. Too often have the same people been called savage and bloodthirsty who, through all experience and by all their traditions regarding armed strangers as enemies, defend themselves and their own with the desperate energy which, as displayed by our own ancestral relations, we term patriotism and courage."
Impurities in Ice.—The once popular theory that water is purified by freezing is, as Mr. Charles Platt shows in Science, not in accordance with facts. While water in its crystalline state should theoretically be nearly pure, still, owing to its formation in needle-like crystals, considerable foreign matter present in the water in suspension may be and is mechanically held within the mass. Another view, that in the freezing of still water a certain concentration of some species of bacteria on the surface of the water may take place, and the first inch of ice may contain these in increased numbers as compared with a sample of water from the same lake, may be well founded, but it is not yet proved that these bacteria have an increased or any vital activity. But when the ice is melted and the temperature of the water is considerably raised, "then we have another problem, that of possible decomposition and organic change in those organisms that may induce results equal to and exceeding those of the bacteria themselves." Disease has undoubtedly, Mr. Platt affirms, been produced by the use of ice from impure sources) and this, too, when mere analysis of the ice in comparison with water standards would not condemn it. But the standards in the analysis of ice must be higher than in that of water. The Massachusetts Board of Health has pointed out that it is not the number of bacteria alone that is to be considered, but their kind, and insists that no water supply that is not fit for drinking purposes should be used as a supply for ice. This is done when ice is gathered from stagnant ponds and sluggish canals that receive the drainage from various sources. Snow ice and ice that has been formed by flooding ice fields with surface water are very liable to be contaminated. In making artificial ice it is customary to use the entire contents of the water tanks. In that case the impurities, repelled at first by the ice forming at the sides of the vessels, are driven to the center and there concentrated, to be at last included in the freezing of the entire mass.
Protection of Orchards against Frost.—According to Charles Howard Shinn, in Garden and Forest, experiments are carried on on a practical scale for the protection of fruit against frost in the orange groves at Riverside, Cal. In some winters the temperature falls so low that the oranges are destroyed or injured. As a remedy the cultivators are using appliances for warming the orchards on a large scale. Their experiments show that the temperature can be raised from four to ten degrees by the use of fires. The moment the thermometer falls to the danger point electric bells can be rung and tanks of crude petroleum lighted. One man has fitted up an eighty-acre orchard at a cost of $10,000 or $12,000. He claims that his grove is absolutely protected, and that the running expense will be very little. Other growers use coal-oil cans filled with kindling wood and coal and placed in the orchard at the rate of from eight to twenty-five per acre. Some provide themselves with two gallon iron kettles and use reduced petroleum. Ten dollars per acre will pay for the plant and the expense of one night's burning. Horticulturists in other citrus colonies are following in the track of Riverside and preparing for future "cold snaps."
Curious Fauna of La Plata.—A curious medley of animal life is described by Mr W. H. Hudson as existing in the pampas region of La Plata: A poisonous toad which kills horses; the wrestler frog, which suddenly pinches its enemy with its fore legs and then runs away; a large, venomous, man-chasing spider, which pursues men on foot and on horseback; dragon flies, a single individual of which will cause clouds of gnats, mosquitoes, and sand flies to disappear in an instant; and an opossum, fully adapted to life in trees, which yet lives in a desert destitute of trees, and when brought to a tree, which it may never have seen before, will clasp it and climb it with all the agility of its forest dwelling relatives of North America.
Manufacture of Fans.—The manufacture of fans is chiefly carried on now in France, Spain, China, Japan, and India. The fashions are established m France principally at Sainte-Geneviève, Audeville, Corbeil-Cerf, Le Déluge, Coudray, and the vicinity of Beauvais and Méru. At Sainte Geneviève they work in bone, mother-of-pearl, and ivory; at Le Petit-Fercourt, and Andecourt, in mother-of-pearl and horn; at Le Déluge and Corbeil-Cerf, pear tree, apple tree, and hornbeam wood; at Boirsière, in bone; and at Paris, in shell. The leaf of the fan is generally made and the fan mounted at Paris. Fans have been made in Spain only for some sixty or seventy years, notably at Madrid, Barcelona, Valencia, Malaga, and Cadiz. Most of the Chinese fans are made in Canton and E-moui, but the manufacture is generally diffused through the country, for the fan is a part of the national costume. Every Chinese of good social standing holds a fan during visits of ceremony, and the custom of writing on fans is spread throughout the empire. The principal centers of production in Japan are the cities of Osaka, Kioto, and Nagoya. In that country the fan is a part of the costume of both sexes, and is to be seen in the hand of the soldier as well as in that of the monk. When a gentleman gives alms to a beggar, he often puts the coin upon his fan; and salutes are made by waving the fan as they are in Europe by tipping the hat. There are also fan factories in some other countries. Lace fans are made at Brussels and De Grammont, in Belgium; fans of braided straw, at Fiesole and Vicenza in Italy; and fan-standards of braided grass and cloth embroidered with gold and silver, in Tunis and Morocco; but France holds the first place in the manufacture of luxurious, and China in that of cheap, fans.
Origin of "Hot Waves."—A theory is published by Prof. F. Hawn, of Leavenworth, Kan., that our southwest winds are tropical currents, which rise to great elevations in the upper atmosphere, and then flow north and reach the ground again in latitude 34°, bringing subtropical heat. As other results of his theory he concludes that the close atmospheric relations between the upper and lower currents attest their common origin; that the atmospheric temperature is incidentally if not perpetually higher in the upper than on the lower levels; that these relatively higher thermal conditions of the upper atmosphere control the lower atmosphere in the spring and summer, and incidentally in the winter; that the hot waves of the Northwest have their origin in a superheated upper atmosphere, and are condensed by gravitation in their descent to the surface, evolving heat in a ratio inverse to the humidity; and that the foehn winds (hot waves), with their resultant temperatures of more than 100° in the temperate seasons and from 65° to 73° in the winter, are not local west of the eighty-eighth meridian, but at intervals simultaneously cover the northern half of the United States.
Qualities of Slates.—From experimental studies with roofing slates, Mr. Mansfield Merriman has drawn the conclusions that those with soft ribbons are of an inferior quality and should not be used in good work; the stronger the slate the greater are its toughness and softness and the less its porosity and corrodibility; softness or liability to abrasion does not indicate inferiority, but is an indication of strength and good weathering qualities. The strongest slate stands highest in weathering qualities, so that a flexural test affords an excellent index of all its properties, particularly if the ultimate deflection and the manner of rupture be noted. The strongest and best slate has the highest percentage of silicates of iron and aluminum, but is not necessarily the lowest in carbonates of lime and magnesia. Chemical analyses give only imperfect conclusions regarding the weathering qualities of slate, and they do not satisfactorily explain the physical properties. The soft roofing slates weigh about one hundred and seventy-three pounds per cubic foot, and the best qualities have a modulus of rupture of from seven thousand to ten thousand pounds per square inch. The test of a slate by balancing it, striking it, and observing its ring is a good one, but is not susceptible of quantitative expression.
Pasteur's Seventieth Birthday.—The seventieth birthday of Louis Pasteur was imposingly celebrated December 27th, in the presence of eminent men of science and statesmen of different countries. The first address was made by the French Minister of Public Instruction, who spoke of the occasion as the "festival of France and of mankind." Addressing M. Pasteur, he said that while his work could be analyzed only by the scientific, the ignorant and the learned alike knew that he had accomplished something great. All his success was due to his unswerving "apostle's faith" in science. Had he devoted himself to pure science, the topmost place would have been his. Happily for himself and for mankind, he deserted that path and henceforth passed his days in inventing antidotes for diseases that had for centuries decimated the animal and human populations. Prof. Joseph Lister acknowledged the obligations of the professors of the healing art to M. Pasteur. Numerous testimonials and offerings of different kinds were presented to M. Pasteur, with a splendid gold medal, the product of an international subscription.
Origin of the Asteroids.—A paper on Groups of Asteroids, by Prof. Daniel Kirkwood, illustrates the theory that these bodies were formed by the resolution of nebulous asteroids. When the number of telescopic planets had grown to hundreds, and when the perihelion distance of some of them had become greater by many millions of miles than the aphelion of others, the theory of explosion was necessarily abandoned. But the doctrine of similarity of origin, the author holds, was not so easily disposed of. The original dimensions of nebulous asteroids were probably many times greater than those of the present bodies. The disrupting tendency of the great bodies of the system, especially when resisted only by the slight central attraction of nebulous asteroids, is easily imagined. Such separation, in short, has no improbability whatever. The dismemberment of comets, as is well known, has actually occurred under our own eyes. Why not also the pulling asunder of nebulous planets? The fact that in many cases the motions of asteroids indicate a common origin, affords strong presumptive evidence in favor of the nebular hypothesis. Possibly, indeed, its true form may have differed from that proposed by Laplace. How many primitive, separate nebulæ were contained in our system, and how many of these primitive masses suffered dismemberment while Mars and the then future earth were yet floating in the solar atmosphere, can not now be told. An indefinite number may, however, undoubtedly be traced. "May not similar processes be also indicated in the slow evolution of binary and multiple stars in the sidereal heavens?"
Early Fans.—The extreme antiquity of fans is attested by their appearance in ancient Egyptian and Assyrian sculptures, where they have the shape of a semicircle with a long handle attached at the center. They were probably used in worship to protect the offerings and sacred objects against contamination by dust and flies. They were known also in India, where they were perhaps introduced from China. The story of their origin in the latter country runs that the daughter of a powerful mandarin was obliged, on account of the heat, to take off her mask during the feast of lanterns, in violation of the law and convention. She shook it rapidly in front of her face, both to give herself air and by the quick motion to veil her identity as fully as possible. Other women followed her example, and the fan was invented. The Chinese historians trace the use of the fan in their country back to a contemporary of Rameses II of Egypt; and it is mentioned by a writer of a thousand years before the Christian era. In ancient Grecian life, a eunuch, in one of the tragedies of Euripides, relates how he waved a fan, "according to the Phrygian fashion," before the hair, face, and bosom of the fair Helen. Fans were early adopted by Roman matrons, who had two kinds—the flabella of ostrich plumes, and the labella of thin woven stuff stretched over a frame. A Roman woman never went out without a slave (flabellifera) whose duty it was to fan her. It is not known whether the fan was used in Europe as an article of the feminine toilet between the fall of the Roman Empire and the eleventh century, for it is not mentioned in that relation; but it was certainly used a great deal in the ceremonies of Roman Catholic worship, when the deacons and the acolytes waved it over the altar at mass. This usage Père Bonami assumes to have traced back to the apostles. Fans are represented in manuscripts and on monuments of the twelfth century and inventories of the fourteenth, under different names, but without specification of their use. They seem to have been disused in the church in the thirteenth century, to appear again after the Crusades in the warmer countries—Spain and Italy—as an accessory to woman's dress; but were not seen in France till the sixteenth century, when they were introduced at court by the Italian perfumers who came in the suite of Catherine de Medicis.
American and African Deserts.—The most striking contrast between the North American "deserts" and those of North Africa is described by Prof. Johannes Walther, of Berlin, as consisting in the far greater wealth of vegetation which characterizes the former. In every direction the eye is met by the yellow-blossoming halophytæ, silver-gray artemisiæ, and prickly cacti; between the opuntias are found cushions of moss, and at the foot of the hills juniper trees seven feet high with trunks a foot thick. Such are the features of the landscape of the deserts of Utah, where plant-growth has completely disappeared only in those places in which the saline complexion of the soil kills vegetation. The Van Horn deserts in western Texas, and the Gila deserts in California are equally rich in vegetation; the altitude of these deserts above the sea-level makes no important difference. Either the mean rainfall in the American deserts is greater than in those of Africa, or else the flora of the American deserts is better adapted to a dry atmosphere. Although the deserts of the two continents present fundamental differences as regards vegetation, there is a surprising similarity between them as regards certain important and characteristic desert phenomena, especially with respect to the topography of the country. There is the prevalence of plains, with mountains rising from them like islands, with no intervening heaps of débris passing from the plains to the steep mountain slopes. This phenomenon is the more striking, as there are no rubbish deltas, even at the outlet of valleys a thousand feet deep. Another feature common to both is the large number of isolated "island" mountains and of amphitheatre formations in the valleys; also the intensive effect of insolation, which splits the rocks and flints, and disintegrates the granite into rubbish. The denuding influence of the wind is visible not only in the characteristics of the surface forms just mentioned, which differ in important points from erosion forms, but it can be directly observed in the mighty dust-storms which rush through the desert. In view of such agreement of important and incidental geological phenomena in regions so remote from each other, the phenomenon of desert formation must be considered to be a telluric process which runs its course according to law, just as the glacial phenomena of the polar zone or cumulative disintegration in the tropics.
Wind Effects.—In a paper on The Wind as a Factor in Geology, published in the Engineer's Magazine, Mr. George P. Merrill, after mentioning several familiar examples of the formation of dunes in Europe, passes to the account of similar phenomena in the United States. In May, 1889, a dust-storm occurred in Dakota during which the soil was torn up to a depth of four or five inches and scattered in all directions; while drifts of sand were formed, several feet deep in favorable places, packed as snow-drifts are packed by a blizzard. In parts of the Western plains the fine, loose sand has been blown away at times, leaving every pebble and large bowlder standing out in bold relief. The loose material often gathers in the form of drifts or dunes, which travel across the country with frequent changes of outline. A few miles north of Winnemucca Lake, in western Nevada, is a belt of these drifting sand hills, described by the geologist Russell as some seventy-five feet in thickness and about forty miles in length by eight miles in breadth. Another range of sand dunes, at least twenty miles long, and forming hills some two or three hundred feet high, is on the eastern end of Alkali Lake in the same State. Dunes of equal height have been formed on the eastern shore of Lake Michigan, and at Grand Haven and Sleeping Bear have drifted over the woodlands, so as to leave only the dead tops of trees exposed. The erosive power of these drifting sands is often an important agent in wearing away the rocks upon which they strike. Carried along by the force of the winds, they work effectively in undermining cliffs, scouring down mountain passes, and giving curious and fantastic forms to prominent rocks.
The Whistled Language of the Canary Islands.—As a result of his studies of the whistled language of Gomera, in the Canary Islands, M. J. Lajard affirms that it is not a special idiom or a whistle which tries to imitate the Spanish language; but it is the Spanish language strengthened by the aid of whistling. "The Gomerian, while he is speaking, puts one, two, or four fingers in his mouth, as we sometimes see done in the street in order to make shrill sounds, and at the same time he whistles with force. There results a mixture of words and whistle, unintelligible to ears not accustomed to it, but in which can be distinguished the words of the language. . . . The whistling, then, is only an artifice employed to carry to a distance the sound of the voice, to the detriment of its distinctness and tone-quality. This last inconvenience is so great that up to this time travelers have been unable to understand the whistled language. To be able to understand it, you must know how to whistle yourself." It is, however, very limited in its compass, and whistled conversations are of short duration. It exists in other of the Canary Islands than in Gomera, and there is reason for believing that it was formerly more widespread and more prevalent than now. Rudiments of a whistled language, the mechanism of which is like that of the Canaries, exist even in Paris; it is employed by butchers and by thieves.
What constitutes a Polluted Water.—A water is said to be polluted, according to Prof, von Pettenkofer, when it is no longer clear and inodorous, when fishes and plants perish in it, and when it contains more organic matter and less oxygen than are to be found in the unpolluted portions of the flow of the stream. Such contamination is essentially different from the transient turbidity due to heavy rains or to melting snow. Still, even the permanent pollutions disappear in the further course of the river bed, by deposition and other agencies. Here the rapidity of the stream and the quantity of the water exert a preponderating effect. The most formidable impurities are supposed to consist of the putrescent refuse which flows out of sewers of cities, and quickly produces an offensive odor at the places where it accumulates. Prof, von Pettenkofer has for many years given his attention to the question of the extent to which rivers are polluted by such agencies, and has had researches conducted by his pupils. But nothing has hitherto altered the opinion which he expressed long ago, that sewage may be safely permitted to flow into a river if its volume is not more than one fifteenth that of the river water, and its rate of flow is decidedly greater than that of the current. Taking the city of Munich, which has 280,000 inhabittants, he computes the pollution of the Isar by its sewage as amounting to only 11000000 of the discharge of the river—a pollution so inconsiderable that it can not be detected by the eye when a corresponding mixture is made up experimentally. But it is also not permanent, for at Ismaning, seven kilometres below Munich, the sewage influx is no longer to be detected; and at Freising, thirty-three kilometres below, the chemical and bacteriological tests show that it has lost nearly all its power of pollution. Thus, the number of 198,000 bacteria per cubic centimetre found by Prausnitz at the mouth of the Munich sewer was reduced at Ismaning to 15,231, and at Freising to 3,602. A similar result was obtained by Frankel with the water of the Spree at and below Berlin. The mere number of bacteria found has, however, no sanitary significance, since these particular microbes are mostly harmless, and in fact destroy the pathogenic microbes in the struggle for existence. The purifying action of rivers is ascribed by von Pettenkofer to the oxygen dissolved in the water in a free state or separated from organisms. In the latter respect the green algae and even non-chlorophyllic plants come prominently into consideration. This vegetation should be preserved; but it may be destroyed by a too great concentration of the water to be purified; and to prevent this, industrial waste waters which destroy vegetation must be kept out till they have been purified.
Bacteriological Processes against Disease.—According to a summary in the Saturday Review, attempts by bacteriological processes to remove from the human system the germs of infectious disease have been made by six different methods. The first is by Pasteur's preventive inoculation, in which a minute quantity of an attenuated culture of the virus is administered to produce a light attack of the disease. The second is M. Pasteur's method in rabies, in which a mitigated virus is injected into a person already attacked with the disease, to overtake it. The third is the employment of the virus of a comparatively mild disease to protect against a more severe one, as in vaccination for smallpox. Next in order is the destruction of the disease-producing bacteria by the administration of antiseptics or bactericides. A fifth method is the re-enforcement of natural means possessed by our systems for combating disease germs: by re-enforcing the leucocytes or white blood-corpuscles, which destroy bacteria, by means of the injection of the blood of animals insusceptible to the disease; by raising or lowering the temperature of the body of the patient; by alterations of diet, climate, or surroundings; or by injection of phagocyte invigorators. The sixth method is by the injection of the "toxalbumens" formed by the bacteria growing in artificial cultures, as is done in Koch's method for tuberculosis. That these methods have not proved entirely satisfactory, and bacteriological treatment is now apparently at a standstill, is not due, it is thought, to any innate defect in the system, but to some technical detail. "When the ingenuity of man has arrived at the point of being able to prove absolutely that organisms, completely invisible to all but the highest magnifying powers attainable, cause each its particular infectious disease; when these tiny things may be made to grow like plants in a garden, separately and in order; when we can keep rows of tubes each with its deadly contents on our laboratory shelves, or in our incubators, like druggists' bottles of inert powders or crystals—surely we shall not stop at this stage in our control over this 'world of the infinitely little.'"