A hand-book of materia medica and therapeutics : with twenty-nine illustrations : being a portion of An analytical compendium of the various branches of medicine / by John Neill and Francis Gurney Smith.

  • Neill, John, 1819-1880.
Date:
1852
Catalogue details

Licence: Public Domain Mark

Credit: A hand-book of materia medica and therapeutics : with twenty-nine illustrations : being a portion of An analytical compendium of the various branches of medicine / by John Neill and Francis Gurney Smith. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    8/101
    cause of the tendency of bodies to fall towards the earth's oentre. The great law of gravitation is, that the attraction is directly as the quantity of matter, and inversely as the square of the distance. This law also regulates the movements of the Bolar system. Capillarity.—This is the attraction exerted between liquids and fine tubes, called capillary, by which the liquid rises in the titbe above the level of the surrounding liquid,—the height depending on the smallness of the diameter of the tube, being inversely to the latter. This is the cause of bodies being wetted when placed in contact with certain liquids, the latter being attracted to the sur- faces of the former. Capillarity is not exerted equally between all solids and liquids; on the contrary, in some cases there is a po i- tive repulsion, as between glass and mercury. The mere density of the liquid does not, however, modify the force. Endosmose.—If a membrane be interposed between two liquids of different density, having an affinity for each other, they will inter- mix by passing through the pores of the membrane. But the rapidity with which the two currents are established, will be un- equal, and will be modified by the membrane. The general law is, that Mc stronger current is from the rarer to the denser li<jni<l. The term Endosmose is at present used to express this stronger current, no matter which direction it may take. It is evidently a modification of Capillarity, though it is influ- enced by the relation subsisting between the membrane and the surface of the liquid. The essential conditions of endosmose are that the liquids should have an affinity for each other, and that one of them, at least, should have an affinity for the membrane. Another physical force, frequently considered as a modification of Endosmose, is the DiffusibUity of Gases, or the tendency of gases to commingle, even though differing in density, and separated by a porous partition. This is readily shown by taking a wide glass tube, and placing in its centre a septum of dry plaster of Paris, and then filling one side of it with oxygen, and the other with hydrogen. The two gases will penetrate the septum, though at very different rates; four cubic inches of hydrogen will pass into the oxygen side, while only one cubic inch of oxygen will pass in the other direc- tion. According to Mr. Graham, the diffusibility of gases is in- versely as the square root of their densities; thus, in the instance above given, the densities of hydrogen and oxygen are to each other as one is to sixteen, hence the diffusive power of the former is four times greater than that of the latter. This law is of great importance in nature, preventing the accumulation of noxious gases in any one spot, and.regulating the intimate mixture of the consti- tuents of the atmosphere. In the process of respiration, the interchange between the oxygen of the air and the carbonic acid of the lungs is effected through