On the _Libri differentiarum sive de proprietate sermonum_--of which the first book is a collection of synonyms, and the second of explanations of metaphysical and religious ideas--see A. Macé's doctoral dissertation, Rennes, 1900. Mommsen has edited the _Chronica majora_ or _Chronicon de sex aetatibus_ (from the creation to A.D. 615) and the "Historia Gothorum, Wandalorum, Sueborum," in the _Monumenta Germaniae historica, auctores antiqitissimi: Chronica minora II_. The history of the Goths is a historical source of the first order. The _De scriptoribus ecclesiasticis_ or better _De viris illustribus_, was a continuation of the work of St Jerome and of Gennadius (cf. G. von Dzialowski in _Kirchengeschichtliche Studien_, iv. (1899). Especially interesting is the _De natura rerum ad Sisebutum regem_, a treatise on astronomy and meteorology, which contained the sum of physical philosophy during the early middle ages. The _Regula monachorum_ of Isidore was adopted by many of the monasteries in Spain during the 7th and 8th centuries. The collection of canons known as the _Isidoriana_ or _Hispalensis_ is not by him, and the following, attributed to him, are of doubtful authenticity: _De ortu ac obitu patrum qui in Scriptura laudibus efferuntur_; _Allegoriae scripturae sacrae et liber numerorum_; _De ordine creaturarum_.
The edition of all of Isidore's works by F. Orevalo (Rome, 1797-1803, 7 vols.), reproduced in Migne, _Patrologia Latina_, 81-84, is carefully edited. See also C. Canal, _San Isidoro, exposicion de sus obras e indicaciones a cerca de la influencia que han ejercido en la civilizacion española_ (Seville, 1897). A list of monographs is in the _Bibliographie_ of Ulysse Chevalier.
ISINGLASS (probably a corruption of the Dutch _huisenblas_, Ger. _Hausenblase_, literally "sturgeon's bladder"), a pure form of commercial gelatin obtained from the swimming bladder or sound of several species of fish. The sturgeon is the most valuable, various species of which, especially _Acipenser stellatus_ (the seuruga), _A. ruthenus_ (the sterlet) and _A. güldenstädtii_ (the ossétr), flourish in the Volga and other Russian rivers, in the Caspian and Black Seas, and in the Arctic Ocean, and yield the "Russian isinglass"; a large fish, _Silurus parkerii_, and probably some other fish, yield the "Brazilian isinglass"; other less definitely characterized fish yield the "Penang" product; while the common cod, the hake and other _Gadidae_ also yield a variety of isinglass. The sounds, having been removed from the fish and cleansed, undergo no other preparation than desiccation or drying, an operation needing much care; but in this process the sounds are subjected to several different treatments. If the sound be unopened the product appears in commerce as "pipe," "purse" or "lump isinglass"; if opened and unfolded, as "leaf" or "honeycomb"; if folded and dried, as "book," and if rolled out, as "ribbon isinglass." Russian isinglass generally appears in commerce as leaf, book, and long and short staple; Brazilian isinglass, from Para and Maranham, as pipe, lump and honeycomb; the latter product, and also the isinglass of Hudson's Bay, Penang, Manila, &c., is darker in colour and less soluble than the Russian product.