For the analysis of cognition-reactions see O. Külpe, Outlines of Psychology (Eng. trans., 1895), pp. 411 foll.; E. B. Titchener, Experimental Psychology (1905), ii. 187 foll. On cognition generally, G. F. Stout’s Analytic Psychology and Manual of Psychology; W. James’s Principles of Psychology (1890), i. 216 foll.; also article [Psychology].
COGNIZANCE (Lat. cognoscere, to know), knowledge, notice, especially judicial notice, the right of trying or considering a case judicially, the exercise of jurisdiction by a court of law. In heraldry a “cognizance” is an emblem, badge or device, used as a distinguishing mark by the body of retainers of a royal or noble house.
COHEN (Hebrew for “priest”), a Jewish family name, implying descent from the ancient Hebrew priests. Many families claiming such descent are, however, not named Cohen. Other forms of the name are Cohn, Cowen, Kahn.
See J. Jacobs, Jewish Encyclopedia, iv. 144.
COHN, FERDINAND JULIUS (1828-1898), German botanist, was born on the 24th of January 1828 at Breslau. He was educated at Breslau and Berlin, and in 1859 became extraordinary, and in 1871 ordinary, professor of botany at Breslau University. He had a remarkable career, owing to his Jewish origin. He was contemporary with N. Pringsheim, and worked with H. R. Goeppert, C. G. Nees von Esenbeck, C. G. Ehrenberg and Johannes Müller. At an early date he exhibited astonishing ability with the microscope, which he did much to improve, and his researches on cell-walls and the growth and contents of plant-cells soon attracted attention, especially as he made remarkable advances in the establishment of an improved cell-theory, discovered the cilia in, and analysed the movements of, zoospores, and pointed out that the protoplasm of the plant-cell and the sarcode of the zoologists were one and the same physical vehicle of life. Although these early researches were especially on the Algae, in which group he instituted marked reforms of the rigid system due to F. T. Kützing, Cohn had already displayed that activity in various departments which made him so famous as an all-round naturalist, his attention at various times being turned to such varied subjects as Aldorovanda, torsion in trees, the nature of waterspouts, the effects of lightning, physiology of seeds, the proteid crystals in the potato, which he discovered, the formation of travertin, the rotatoria, luminous worms, &c.
It is, however, in the introduction of the strict biological and philosophical analysis of the life-histories of the lower and most minute forms of life that Cohn’s greatest achievements consist, for he applied to these organisms the principle that we can only know the phases of growth of microscopic plants by watching every stage of development under the microscope, just as we learn how different are the youthful and adult appearances of an oak or a fern by direct observation. The success with which he attempted and carried out the application of cultural and developmental methods on the Algae, Fungi and Bacteria can only be fully appreciated by those familiar with the minute size and elusive evolutions of these organisms, and with the limited appliances at Cohn’s command. Nevertheless his account of the life-histories of Protococcus (1850), Stephanosphaera (1852), Volvox (1856 and 1875), Hydrodictyon (1861), and Sphaeroplea (1855-1857) among the Algae have never been put aside. The first is a model of what a study in development should be; the last shares with G. Thuret’s studies on Fucus and Pringsheim’s on Vaucheria the merit of establishing the existence of a sexual process in Algae. Among the Fungi Cohn contributed important researches on Pilobolus (1851), Empusa (1855), Tarichium (1869), as well as valuable work on the nature of parasitism of Algae and Fungi.
It is as the founder of bacteriology that Cohn’s most striking claims to recognition will be established. He seems to have been always attracted particularly by curious problems of fermentation and coloration due to the most minute forms of life, as evinced by his papers on Monas prodigiosa (1850) and “Über blutähnliche Färbungen” (1850), on infusoria (1851 and 1852), on organisms in drinking-water (1853), “Die Wunder des Blutes” (1854), and had already published several works on insect epidemics (1869-1870) and on plant diseases, when his first specially bacteriological memoir (Crenothrix) appeared in the journal, Beiträge zur Biologie, which he then started (1870-1871), and which has since become so renowned. Investigations on other branches of bacteriology soon followed, among which “Organismen der Pockenlymphe” (1872) and “Untersuchungen über Bacterien” (1872-1875) are most important, and laid the foundations of the new department of science which has now its own laboratories, literature and workers specially devoted to its extension in all directions. When it is remembered that Cohn brought out and helped R. Koch in publishing his celebrated paper on Anthrax (1876), the first clearly worked out case of a bacterial disease, the significance of his influence on bacteriology becomes apparent.