828 P R P R O siege of Rhodes by Demetrius Poliorcetes (305-4 B.C.) notwithstanding that the garden in which he painted was in the middle of the enemy s camp. Demetrius unsolicited took measures for his safety ; more than that, when told that the lalysus just mentioned was in a part of the town exposed to assault, Demetrius changed his plan of opera tions. Possibly the slowness and laboriousness of the work of Protogenes was due partly to a want of training in his youth. .He appears to have been self-taught ; some said that he had begun life as a ship-painter, and, though the painting of certain small figures of ships in a picture of his in Athens, however excellent it may have been, can hardly be held to confirm this account of his youth, it does not on the other hand render the account unreliable. It may have been due also to a want of early training that he found so much difficulty in rendering the foam at the mouth of a dog which occurred in the picture of lalysus. Angry at his many failures, he dashed the sponge wet with the white colour which he had just wiped off at the mouth of the dog. The result was a perfectly successful foam. lalysus was a local hero, the founder of the town of the same name in the island of Rhodes, and probably he was represented as a huntsman. The picture was still in Rhodes in the time of Cicero, but was afterwards removed to Rome, where it perished in the burning of the temple of Peace. On another occasion Protogenes seems to have used his sponge with a different effect. The picture painted during the siege of Rhodes consisted of a satyr leaning idly against a pillar on which was a figure of a partridge so life-like that ordinary spectators saw nothing but it. Enraged on this account, the painter wiped out the partridge. The Satyr must have been one of his last works. He would then be about seventy years of age, and had enjoyed for about twenty years a reputation next only to that of Apelles, his friend and benefactor. Both were finished colourists so far as the fresco-painting of their day permitted, and both were laborious in the practice of draw ing, doubtless with the view to obtaining bold effects of perspective as well as fineness of outline. It was an illus tration of this practice when Apelles, finding in the house of Protogenes a large panel ready prepared for a picture, drew upon it with a brush a very fine line which he said would tell sufficiently who had called. Protogenes on his return home took a brush with a different colour and drew a still finer line along that of Apelles dividing it in two. Apelles called again ; and, thus challenged, drew with a third colour another line within that of Protogenes, who then admitted himself surpassed. This panel was seen by Pliny (JV.//., xxxv. 83) in Rome, where it was much admired, and where it perished by fire. In the gallery of the Propyliea at Athens was to be seen the panel by Protogenes in which occurred the figures of ships already mentioned. The subject consisted of two figures representing personifications of the coast of Attica, Paralus and Hammonias, to whom the presence of ships would be the more appropriate as the Athenians actually possessed two ships so named. For the council chamber at Athens he painted figures of the Thesmothetae, but in what form or character is not known. Probably these works were executed in Athens, and it may have been then that he met Aristotle, who recommended him to take for subjects the deeds of Alexander the Great. In his Alexander and Pan he may have followed that advice in the idealizing spirit to which he was accustomed. To this spirit must be traced also his Cydippe and Tlepolemus, legendary personages of Rhodes. Among his portraits are mentioned those of the mother of Aristotle, Philiscus the tragic poet, and King Anti- gonus. But Protogenes was also a sculptor to some extent, and made several bronze statues of athletes, armed figures, huntsmen, and persons in the act of offering sacrifices. PROTOPLASM. In most of the biological articles already before the reader, whether concerned with general questions, as BIOLOGY, ANATOMY, BOTANY, EMBRY OLOGY, EVOLUTION, HISTOLOGY, MORPHOLOGY, PHYSIOLOGY, &c., or even with special groups of living beings, as ANIMAL KINGDOM, FORAMINIFERA, FUNGUS, PROTOZOA, <tc., special reference has been made to protoplasm as the living matter from which all kinds of living beings are formed and developed, and to the properties of which all their functions are ultimately referred. Fundamentally important then as this substance is, whether we occupy the standpoint of morphology, physiology, or aetiology, an attempt must be made to outline the way in which our knowledge of it has been reached, to bring together by the aid of a short summary the statements of such preceding articles, and to supply means of extending the general idea thus obtained by reference to the original literature of the subject. 1. History. Among the varied and fruitful observa tions of the early microscopists, Rosel v. Rosenhof s ex cellent account (1755) of his "Proteus animalcule" (the. familiar Amoeba) is especially noteworthy as the earliest description of the form and movements of what we now know as a mass of living protoplasm. Such discoveries as those of rotation in the cell of Chara (Corti, 1772), and of similar movements in other plant cells ( Vallisneria, Meyen, 1827; Tradescantia, R. Brown, 1831), are also memorable, more so indeed in this relation than is the great contemporaneous movement in general histology, since this, though aided by the rapid improvement of the microscope, eagerly carried on by the united labours of zoologists and botanists, headed by Johannes Miiller and Robert Brown, and culminating in the hands of Schleiden and Schwann (1838-39) in the fundamental morphologi cal generalization of the cell theory (see MORPHOLOGY), included views of the structure, origin, and function of the cell-substance alike erroneous and misleading. Know ledge had in fact to start afresh from the level of the unappreciated discovery of Rosenhof ; and it is accordingly from the observations of Dujardin on Foraminifera (1835) that our modern knowledge of protoplasm dates. His main account is still worth reading in his own words. In proposing the term "sarcode," he says, "je propose de nommer ainsi ce que d autres observateurs ont appele uno gelce vivante, cette substance glutineuse, diaphane, in soluble dans 1 eau, se contractant en masses globuleuses, s attachant aux aiguilles de dissection, et se laissant <Stirer comme du mucus, enfin se trouvant dans tous les animaux inferieurs interposed aux autres elements de structure." Though thus dissipating many errors, and placing the study of the lowest forms of life on its true basis, Dujardin unfortunately did not see the full bearing of his discovery. He recognized his sarcode, however, in the polyps, and noted that the ova of the slug exhibited similar move ments. The next important step was not taken until 1846, when the botanist Hugo von Mohl, working on quite independent lines, reached a clearly defined conception of the vegetable cell, not only, as usual hitherto, distinguish ing the cell wall and the nucleus from the cell contents (Zdlsaft), but also the "tough, slimy, granular, semi fluid " constituent from the watery cell-sap hitherto generally confused with it under the common name. For this substance (which Schleiden had already vaguely men tioned as "Schleim") he proposed the term "protoplasma" (717x07-05, first, TrAacr/xa, formed substance). The discovery of the amoeboid movements of colourless blood corpuscles dates from the same year, and the basis was thus prepared for Ecker s acute comparison (1849) of the "formed contractile substance " of muscle with the " unformed contractile
substance" of the lowest types of animal life. This