PROTOPLASM. 472 PROTOTHERIA. sides pioteids protopIaMu contains small pro- portioirs of mineral matters, especially phos- phates and sulphates of potassium, calcium, and magnesiiim, as well as sodium, iron, phosphorus, and chlorine found in the ash. It is dissolved by prolonged treatment with weak acids or alkalies. Strong alcohol coagulates it, as docs heat. Proteids are unstable, and protoplasm, es- pecially that of animal cells, decomposes with more or less rapidity and gives out a fetid odor. Protoplasm readily "stains by the application of neutral or slightly alkaline solutions of carmine, logwood, or acid aniline dyes (eosin and acid fuchsin). Thus by the use of a carmine stain the chromatin in cells is clearly demonstrated. Pro- toplasm is usually, but not always, alkaline in reaction : red litmus paper is turned blue by it: Protoplasm is evidently a highly couiplex sub- stance, but it is not known whether it is a definite chemical body, or whether it is a varying mix- ture of diflerent chemical substances. "Proto- plasm." says Hertwig, "is not a chemical, but a morphological conception," and the present or- ganization of protoplasm is "the result of an exceedingly long process of development." For remarks upon the origin of protoplasm, see Spon- taneous Genekation. General PRorERTiE.s of Protoplasm. If we watch an amoeba under the microscope we gather that protopla.sm first of all is contractile and irritable: that it assimilates its food, and is ca- pable of excreting the waste residue ; that it even respires, while it reproduces true to its species by self-division. Under a high power of the micro- scojx' the protoplasm of the egg of a starfish or sea-urchin, says Wilson, gives the appearance of a, fine mesliwork or framework composed of innu- merable minut* granules, or microsomes, sus- pended in a clearer, less deeply staining, continu- ous substance. The spaces of the •meshwork { filar substance, spongioplasra, cell-reticulum ) are filled with a clear, homogeneous substance, not staining readily, and called the ground-sub- stance ( interfilar substance, euchylema). MOVESIENT and IRRITABILITY OF PrOTOPLASXI. Tliis consists of the changes in the form of the body. e.g. of the amoeba, or of the white blood-eorpuscles ( leucocytes ) , whence such move- ments are called 'amtpboid:' while in the interior streams of granules are seen passing along the body and in the psevidopods. That irritability exists is proved by many facts, as that amceboid movements and the flow of granules can be in- duced, stopped, or modified by mechanical, chemi- cal, and thermal stimuli. Nutrition and As.similatiox. Irritability and the power of motion are essential in bring- ing about assimilation, which is the change of food substance into protoplasm. !Most unicellu- lar animals, as well as the white amoeboid blood- corpuscles, and certain cells in sponges, coelen- terates, etc., have been observed to take in or de- vour solid substances. They take the particles of food into the midst of the protoplasm of their bodies by flowing around them: they extract all the assimilable .and reject the indigestible portions. (SeeAiirEBA.) ^lany Protozoa (q.v.) , besides taking in food for their own growth and for replacing worn-out parts, have the power of producing substances, such as lime or silica, or in rare cases cellulose, forming hard coverings or sLells, often many-chambered and wonderfully complex, as well as frequent 13- richly ornamented. This formative power, says Hertwig, is the start- ing point in the foimation of tissue. History of the Discovery of Protoplasm. In the eighteenth century Corti (1772) and later Treviranus (1807) had seen that the grains of chlorophyll which cause the green color of plants flow rapidl.v in the. interior of cells of certain plants. Mohl discovered that this ap- parent motion of the chlorophyll grains was due to that of the substance in which they were con- tained. This substance Mohl in 184G called ■protoplasm.' while several observers (Siebold, Kolliker, Remak, etc.) afterwards discovered movements similar to those seen in vegetable protoplasm in the lymph corpuscles of animals, and therefore Remak applied the same term 'protoplasm' to the fundamental subst,ance of animal cells. Meanwhile further knowledge of ]irotoplasni was obtained by the study of certain Protozoa, and Dujardin in 18.35 applied the name 'sarcode' to the gelatinous granular contractile substance forming their bodies. Ferdinand Cohn in 1850 argued for the identity of 'sarcode' and 'protoplasm.' Finally iliix Schultze in 1801, and De Bary, as the result of jirolonged investiga- tions, proved,.the identity of the protoplasm of plants and animals with the sarcode of the Pro-- tozoa. Afterwards the cell membrane was found by Xiigeii, Leydig, Kcilliker, Cohn, etc., to be of minor importance, the protoplasm being the es- sential, dynamic substance of the cell. Bibliography. Dujardin, Recherchcs sur les organismes infcrieiirs {Annales des Sciences iVa- turcllcs. Paris. 1835-36) : O. Hertwig. The Cell (New York. 1805) ; Yilson. The Cell' in Develop- ment and 'Inheritance (ib., 1900) ; Verworn, Oen- eral Physiology ( ib., 1899). PROTOROHIPPUS (Xeo-Lat., from Gk. irpuTos. prOtos, first -j- 8pos, oros, mountain + iVTTos, hippos, horse). An ancestor of the horse in the Middle Eocene Period. See Horse, Fossil. PROTOROSAURI. See Prosauria. PROTOSPONGI A ( Xeo-Lat., from Gk. irpuroj, protos. first + 0-^077/0, spongia, sponge). One of the earliest, if not the earliest, fossil sponges known. It consisted of a spherical body which now appears as a faint 'disk upon the surface of the rock, with the skeleton showing as a regular network of cross-shaped spicules that form square meshes. It is found in the Cambrian for- mations of North America and Europe. PROTOTHERIA (Xeo-Lat. nom. pi., from Gk. irpSiTOi^iirfttos, first + 0-qplov, therion. diminu- tive of 8rip,th{i; wild beast). The lesser and inferior of the two primary divisions of the Mammalia. It embraces only the small group represented at present by the Australian and Papuan egg-laying duckbill and echidnas, which constitute the order ilonotremata (or Ornitho- delphia ) : and possibly also the doubtful and little-known fossil group termed Allotlieria or Multituberculata. The mammalian affinities of these extinct forms have been denied by some paleontologists, but the weight of opinion views them as properly included in that category. Both externally and internally the monotremes show much that is distinctly mammalian, including the character of the brain, which in the echidnas at least is surprisingly large and well convoluted. The absence of a corpus callosuni is the chief peculiarity differentiating it from the eutherian
