BLOCH, Mark Eleazar, an ichthyologist and helminthologist, born at Anspach about the year 1730. He was of the Jewish nation, and his parents being indigent, his early education was much neglected; but having entered into the employment of a surgeon at Hamburg, he supplied the deficiency by his own exertions, and made great progress in the study of anatomy, as well as in the other departments of the medical sciences. He established himself as a physician at Berlin, and found means to collect there a valuable museum of the subjects of all the three kingdoms of nature, as well as an extensive library; and these objects often attracted to his house an assemblage of the most accomplished naturalists of his age and country.

He applied himself, however, more particularly to those parts of natural history which are the most connected with the practice of physic; and, on occasion of a prize question of the academy of Copenhagen, he entered into a very elaborate examination of the different species of worms which are found in the bodies of other animals. In his essay on this subject, to which the prize was adjudged, he maintains that the parasitical species are only found within the animal body; and since they often occur in the foetus, and in cavities which are completely inclosed, he infers that they must be generated in some unknown way, and not taken in with the food in the form of eggs. For the general remedy in cases of worms in the intestinal canal, he recommends large draughts of cold water, followed by cathartics. He has added to his Essay a complete classification and description of all the species of intestinal worms, accompanied by figures.

Μ. Bloch also published a variety of papers on different subjects of natural history, and of comparative anatomy and physiology, in the collections of the various academies of Germany, Holland, and Russia, particularly in that of the Friendly Society of Naturalists at Berlin. But his great work was his Ichthyology, which occupied the labour of a considerable portion of his life. His attention was first directed to the subject by receiving a present of a species of salmon, which he could not find described in the Linnaean System of Nature; and he discovered a number of similar omissions in Artedi, and in all former ichthyologists. He accordingly undertook to collect into one work everything that was known respecting the natural history of fishes, and to give figures of all the species; and he passed several summers by the sea side, and among fishermen and their nets, comparing the descriptions of authors with nature, and taking bold sketches of the most interesting subjects, not uncommonly on board of the very boats which furnished them. His publication was encouraged by a large subscription, and it passed rapidly through five editions in German and in French. He made little or no alteration in the systematical arrangement of Artedi and Linné, although he was disposed to introduce some modifications into the classification, depending on the structure of the gills, especially on the presence or absence of a fifth gill, without a bony arch; a character which affords some useful subdivisions of several genera. To the number of genera before established, he found it necessary to add nineteen new ones; and he described 176 new species, many of them inhabitants of the remotest parts of the ocean; and by the brilliancy of their colours, or the singularity of their forms, as much objects of popular admiration as of scientific curiosity.

In 1797 he paid a visit to Paris, where he was secure of finding a variety of collections of such subjects of natural history as had been inaccessible to him on the shores of the Baltic; and he returned to Berlin by way of Holland. FIis health, w,hich had hitherto been unimpaired, began now to decline. He went to Carlsbad for its recovery, but his constitution was exhausted, and he died there on the 6th of August 1799. (Coquebert in Rapport de la Société Philomathique, vol. iv. 8vo, Par. 1800.) (l. l.)