FILTER AND FILTRATION. Gin FIN. adhesion, makes it more difficult for the sus- pended matters to pass through. Another con- tributing cause is the tortuous passage through the filtering material, the several particles of the latter serving as so many dams or barriers to the progress of the suspended matters, adhesion and agglutination also aiding in this process. The speed or capacity of filters, and also their effi- ciency or thoroughness, may be aided in some cases by the use of a coagulant, which serves to bring the suspended matters together in flakes or clots which are readily retained by the filter- ing material. The burden upon filters, or their tendency to elog, may be lessened in some cases by previous sedimentation. When filters de- teriorate so they give a filtrate deficient in qual- ity or quantity, they may be either discarded or cleaned, according to their nature. Sometimes they may be washed by reversing the flow of liquid through them. See Sewage Disposal; Water Purification. FILTER PRESSES. A combination of strainers or filters with some form of press de- signed to hasten the process or increase the thor- oughness of separating liquids and solids. In many cases the filtering is nominal only, the filter cloth being used chiefly to retain the solid matter, which otherwise would be squeezed out between the plates or racks of the press. The force used in pressing may be applied by hand, steam, or other power, by means of simple screws or more or less complicated gearing, or air-pressure may be used. Common examples of the former ave the ordinary cheese and cider presses, and tankage presses used in garbage and fat rendering establishments. Compressed air is sometimes used both to fill and operate presses dealing with matter having a high percentage of water, like sewage sludge. (See Sewage Dis- posal.) Hydraulic power may also be used to operate filter presses. FILTH DISEASE. A term that may be ap- plied to any disease caused or supported by ac- cumulation of filth. The term, although useful, is not strictly scientific. It has been applied to typhoid fever, cholera, dysentery, and diarrhoea, as well as to erysipelas, pyaemia, septicaemia, and puerperal fever. These were called 'filth diseases,' on the supposition that they were caused by putrefying excrement, garbage and refuse, leakage and seepage from cesspools, privy vaults, and sewers, through which wells and springs, as well as the atmosphere, may become polluted and cause disease. Since the discovery that the causative principle in each of these dis - is a specific bacillus, the term 'filth dis- eases' has fallen into partial disuse. It is known that bacteria do not pass through the air ac- companying the vapor arising from a Quid, and that, in general, gases and vapors cannot convey infection, bacteria being spra or dust. 5ce1 it is true that allowing filth, particularly human excrement, to accumulate so that it may gain access to drinking va may attracl insects which will carry it about, is to invite contamination and infection by the bacteria d may exisi in such filth. Thus, flies may carry frecal matter aboul and transfer it to i Typhoid fever is spread through the medi- , or milk or othei food which has been contaminated by the excremenl of patients suffering with the di ea e Wan! of personal cleanliness may encourage disease, and an ac- cumulation of refuse affords a nidus for the multiplication of pathogenic germs. It is there- fore clear that preventing the accumulation of filth must in a large measure serve to prevent also filth diseases. See Insects, Propagation of Diseases by; Typhoid Feveb. FILUM AQDa: (Lat., thread of the stream). In law, the imaginary line, running along the centre of a natural stream, which is the presump- tive boundary between the lands on the opposing shores. When one conveys lands bounded by a watercourse, he is presumed, if the stream be private and the bed of it is vested in the grantor, to convey to the centre or thread of the stream. This presumption may be rebutted by a plain ex- pression of a contrary intention in the deed, or the whole of the stream may be granted with the land on either side. But where, as is usually the case, a stream is taken as the boundary with- out special restriction, it is the thread, or filum aquas, which is understood as the line between the riparian owners. This thread has no refer- ence to the position of the channel (q.v. ), nor does its location follow the flow of the water; but it is, as a general thing, a line midway be- tween the banks and following the contour of the shore as nearly as possible. The principle of the filum aquas finds its most frequent illustra- tion in the case of riparian proprietors in pri- vate streams, but it is equally applicable to the delimitation of frontiers between opposing States or minor political divisions. See Riparian Rights. FIMBRIATED (Lat. fimbriatus, fringed, from fimbria, border, fringe). A term in her- aldry, applied to an ordinary having a narrow border or edging of another tincture. FIN (AS. film; connected with Lat. pinna. fin). An organ possessed by aquatic animals and used for locomotion in the water. General Considerations. Fins are cutaneous folds which may or may not be supported by fin- rays or other framework. In the squid the fins are cutaneous lobes; in pleuropods they are morphologically paired parts of the foot. Folds of skin occur on the tails of certain adult and larval Amphibia. The fore legs or 'flippers' of marine turtles and cetaceans are modified into a fin-like organ, besides which the tail of ceta- ceans ends in a fin, and a fatty dorsal fin may also lie present. The tins of both turtles and ceta ccans are supported by a bony framework. Fins op Fishes. Fishes' tins may consist of mere f. i)<ls of the skin, or these membranous folds may he supported by cartilaginous or bonj rods, the fin rays. When the supporting rays are unsegmented, in which ease they are usuallj strong, we have a spin; rayed fin like the firs! dorsal of the perch; the whole or a part of B 'jhen fin may be spiny raxed. Sneh li>lies are classed as 'acanthopterous.' When the rays are see iited. we have Bofl raved fins, and the fishes possessing only sueh are classed as 'mala copterous.' Fins arise as folds of the skin. In young fishes these folds are much more exten sive, and later disappear, except in the re where the permanent Bns are to develop. For the whollj different fins of certain ancient fishes and the fev existing lung-fishes, see Dipnoi. Fin- are of two kinds — paired and unpaired. The paired fins, placed at or near the vent i ill
