Sewerage

or minute forms of vegetable life that exist in the absence of air. Artificial beds for the final treatment of sewage are classed as contact beds, intermittent sand filters, and percolating filters. Contact beds consist of broken stone, cinders or clinkers, coke and other materials, ranging in size from 1 or 2 in. to in., contained in water-tight compartments. The beds are filled, stand full (hence the term contact), are emptied, and then rest, the cycle taking from 4 to 8 or 12 hours. Intermittent sand filters have free underdrains. The sewage is applied for a few hours or days, and then the beds are given a rest. Percolating filters are composed of large stone, clinker or other material, which the sewage is sprayed and through which it percolates, continuously. The action in all three classes of filters depends upon aerobic bacteria, or those working in the presence of air. The septic tank and the various filters described, particularly contact beds and percolating filters, have come to the front since about 1895 (intermittent filters much earlier), and are classed as bacterial processes. No commercially practicable method of sewage treatment can convert sewage into drinking water.

on

The volume of sewage proper to be carried off depends on the water consumption of the district, and amounts usually to from 30 or 35 gallons per head of the population in Great Britain, and 100 gallons or more in the United States. The flow, however, varies in volume throughout the twentyfour hours. Mr. Santo Crimp, in his book on Sewage Disposal Works (2d ed. 1894), states that 70 per cent. of the total flow may be discharged in twelve hours, and 8 per cent. in one hour, during the period of maximum flow. Storm overflows are frequently constructed at suitable points throughout the system, by which part of the water brought down in times of heavy rain is discharged into the nearest river or stream. The metropolitan sewers in London were designed to carry off in the urban districts a volume of storm water equal to a rainfall of in. per twenty-four hours, in addition to the ordinary sewage, and half that amount in the suburban districts. The storm overhows on the outfall sewers constructed for the city of Glasgow do not come into operation until the sewers are carrying a volume of storm water equal to a rainfall of in. per twenty-four hours. The heavier downpours of rain in America call for greater storm sewer facilities than vided in Great Britain. See Latham's Sanitary Engineering

are pro

125

(ed. 1878), and Robinson's Sewerage and Sewage Disposal (2d ed. 1905). For. ulæ and other information for 'he design of sewerage cystems will be found in Moore's Sanit ry Engineering (ed. 1901); Folwell's Sewerage (1904); Ogden's Sewer. Design (1903); and Baker's Sewerage and Sewage Disposal. For sewage treatment sc, in addition, Rafter and Baker's Sewage Disposal in the United States (1894); Rideal's Sewage and the Bacterial Purification of Sewage (1901); Barwise's The Purification of Sewage (1904); Baker's British Sewage Works (1905).

Sewickley, bor., Allegheny co., Pa., 13 m. w.N.w. of Pittsburg, on the N. bank of the Ohio R., and on the Pitts., Fort Wayne and Chi. div. of the Pa. R. R. It is a residential borough and a summer resort. Natural gas and petroleum occur in the district. The borough has a public library. A fresh-air home is supported. The borough was incorporated in 1853. Pop. (1910) 4,479.

Sewing. See NEEDLEWORK and SEWING MACHINE.

Sewing Machine. The first practicable sewing machine was invented by Thomas Saint, in England, in 1790. Although crude in construction, it embodied many of the essential features of the modern sewing machine, including the horizontal feed-plate, the overhanging arm carrying a vertically descending needle, and the automatic feed; this machine produced the crochetstitch. A machine patented by Thimonnier in France in 1830 was employed for making uniforms in Paris in 1841. In that year, in England, Newton and Archbold patented a chain-stitch machine, employing for the first time the eye-pointed needle. The real development of the sewing machine as a competitor with hand labor begins with the machine patented by Elias Howe, Sept. 10, 1846. Howe's machine combined the eye-pointed needle with the shuttle for forming the stitch, and the intermittent feed for supplying the material to be sewn. Although his patents were at first infringed upon, and he himself reduced to abject poverty, Howe finally succeeded in establishing his rights to his invention, and amassed an enormous fortune from his royalties. The next important improvement in the sewing machine was the invention of the four-motion feed by A. B. Wilson in 1850. This feed is still the only one in general use. Prior to 1850 all machines had employed an overhanging arm which held the needle directly, and which vibrated with it. But in 1851 Isaac M. Singer, of New York, patented the first

Sewing Machine

rigid-arm sewing machine; he also made important improvements in the shuttle. This machine of Singer's has formed the basis for all the sewing machines since manufactured.

or

Sewing machines are of two classes those for domestic use, usually driven by treadle hand, and machines of special construction, driven by power, for use in the various industries. The principle upon which the machine works is the same in all types: the needle is clamped to a bar or arm which moves vertically up and down at great speed, piercing the material to be stitched, which is placed upon a flat or curved steel plate. The needle is made with the eye near the point, the eye passing through the material, which is moved automatically for a small distance at a time, to form the stitch. Two kinds of stitches are chiefly in use the single-thread or chain stitch, which can be unravelled by pulling the end of the thread, and the double-thread or lock stitch, in which an upper and lower thread are used, locking together in the centre of the material; this stitch cannot be unravelled, but must be cut through if the material is to be taken apart. The operation of the chain-stitch machine is as follows: The needle descends through the material and throws out a loop of thread, which is seized underneath and held by a hook-shaped piece of steel called a looper, which has a vibrating or rotating movement. The needle then rises, and as soon as it is clear of the material this is moved forward the given length of the stitch. The looper then spreads the loop of thread across the path of the needle; this descends again through the loop, which slips off the looper and is drawn tightly up to the under side of the material. The needle next throws out a new loop, which is seized by the looper, and the operation proceeds as before. The appearance of the stitch is as a straight line on the upper surface, and as a series of interlocked loops on the under side. The operation of the lock-stitch machine is as follows: The needle descends and throws out a loop as before; through the loop a second thread is passed by a vibrating shuttle, or the loop is passed over the under spool of thread by a steel circular hook having a rotating movement. When the needle rises, the second thread is drawn tightly up to the under side of the material, and the two threads interlock together in the centre. To facilitate the formation of the loop, and to permit the under thread to be passed through it, the needle is

to various algæ and fungi, Klebs has shown conclusively that certain external conditions (of nutrition, moisture, light, temperature, and chemical reagents) may determine the Occurrence of asexual reproduction by ZOOspores which require no fertilization, while others as certainly evoke sexual reproduction by gametes which conjugate.

Nature of Sex. When we keep to the lower reaches of sex expression, we find that the problem resolves itself into this: Of two ova of the same mother fertilized by spermatozoa of the same father, one develops into an eggbearing animal and the other into a sperm-bearing animal; there may be no other visible difference between them, either in structure or in function, but what is it that determines the respective femaleness and maleness? In our opinion, the only fundamental difference is a slight difference in the physiological 'gearing,' in the life-ratio between anabolic and katabolic processes-i.e. between constructive and disruptive, assimilative and dissimilative vital changes. If a plant and an animal of equal weight be contrasted, the ratio of anabolism to katabolism in the plant is K greater than the corresponding ratio in the animal; and the same may be true of the fundamental contrast between female and male organisms. But just as dimorphic varieties arise and become established in a species, so it may be that an incipient sexual dimorphism arose long ago, based on a slight bias to one side or the other in the physiological gearing.

a

There are various reasons why this initial dimorphism, once started, should continue, and should be gradually more and It tended to more accentuated. secure cross-fertilization, which implies the union or amphimixis of more or less diverse germplasms. This not only helps to swamp undesirable germinal idiosyncrasies, but to induce possibly advantageous new variations; for while there are parthenogenetic forms, some of which are variable, and while there are self-fertilizing (or autogamous) hermaphrodite forms, like some flukes and tapeworms and various plants, the numerous arrangements throughout animal and plant kingdoms for securing cross-fertilization show that there must be decided advantage in exogamous amphimixis. The advantage as regards some plants has been proved by Darwin and others; the advantage as regards animals is hinted at by the occasionally dire results of too prolonged and intimate in

the

breeding; and the extreme form of inbreeding may be said to be self-fertilization.

The next step in the argument is perhaps more difficult, and it is certainly less capable of experimental verification. In most of the relatively simple multicellular animals, such as sponges and zoophytes, there is nothing analogous to sexual union; the fertilization of the ova by the spermatozoa is left, roughly speaking, to chance. Even in many complex forms, such as seaurchins and bivalves, the sperms are usually liberated into the water to find or not to find the similarly liberated ova. In such cases there is little sexual dimorphism, though there are sometimes special arrangements for the equipment of the ova with yolk, and the like. On the other hand, in actively moving animals ranging over a more or less extensive habitat, and not very closely gregarious, the fertilization of the ova could not be left to chance, and gradually, we presume, those variations in males and females were selected which were most effective in securing amphimixis-that is, practically, in producing offspring. Thus arose the almost endless intricacy of sexual dimorphism-all manner of arrangements for tracking and seizing the females, for attracting the males, for transferring and receiving the sperm.

In short, sexual dimorphism arose as an adaptation for securing amphimixis, and had its physiological side in sexual appetency and mating instincts, as well as is structural aspect in the specialization of particular organs. We thus reach the view that almost all the details of sex-differences are adaptations, originating in the germinal variations of particular males and females, and established by natural selection in one or other of its many modes, including sexual selection.

Let us suppose that a particular male (or set of males) shows, as the result of germinal variations, some quality advantageous in mating: the progeny inheriting this quality will be similarly at an advantage, and the quality will gradually become dominant in proportion to its value. The same will hold good in regard to variations in the females. Now the inheritance must be multiple; it must, on Weiss ann's argument, from which we see no escape, consist, not of a single set of representative primary constituents or determinants for the various structures of the body that is to develop, but of several alternative sets. Thus drone bees, with their masculine peculiarities, have no father; the ova which their

spermatozoa

fertilize develop

into queens (females) or workers (sterile females).

When we take a survey of a large number of cases of sexual dimorphism, and observe, for instance, that the females are often larger, less active, less brightly colored, with a longer life and so on, and, conversely, that the males are often smaller, more energetic, more decorative, and of shorter life, we are tempted to regard the two sexes simply as expressions of different physiological diatheses, as literal embodiments of the obvious contrast between ovum and spermatozoon. We know, moreover, that subtle influences pass from the reproductive organs to the remotest parts of the body, and that the removal of the reproductive organs may be followed by the appearance of feminine characters in a male or of masculine characters in a female. Moreover, there are cases where distinctive masculine or feminine secondary characters can be shown with some plausibility to be physiologically correlated with the general constitutional contrast between egg-producer and spermproducer. But while we adhere to the view that the fundamental difference between male and female is a difference in the protoplasmic gearing or rhythm of metabolism the phraseology must remain vague-yet it does not appear that we can in any way dispense with the complementary view that the details of sex-dimorphism are the results of long processes of selection. Thus we arrive at a combination of the physiological and the adaptational theories of sexual dimorphism.

sex.'

Another difficult question is that generally referred to under the phrase the 'determination of What determines whether an egg is to develop into a male or a female organism? On the one hand, most of the careful experiments and observations on mammals lead to the conclusion that the sex of the offspring is fixed ab initio by the constitution of the egg. In other words, there are ova whose organization' (to put it statically), or 'metabolic bias' (to put it kinetically), is such that they will develop into male or female organisms no matter what natural influences may be brought to bear on them. They are predetermined from the first, and their bias cannot be altered. Thus, in the case of mice, no alterations of nutrition, prolonged through two generations, seem to make the least difference in the proportion of male and female progeny. Moreover, cases are alleged where a mother produced only daughters,