PROTOPOPOFF 



among the meshes of this net- 

 work is a clear semi-fluid substance 

 termed the hyaloplasm, which pos- 

 sibly acts as a nutrient material 

 for the network. The spongio- 

 plasm is contractile and elastic, 

 and is often seen to be in very 

 active movement. At the begin- 

 ning of the 19th century various 

 biologists observed that the cell 

 contents of certain algae become 

 extruded in jelly-like globules, 

 which swim about independently 

 in water for a time, ultimately 

 coming to rest and growing into 

 new algae. 



About 1826 a detailed study 

 of the alga Vaucheria led to the 

 discovery that there are certain 

 plants which during their develop- 

 ment pass through this motile stage 

 as little globules, and about the 

 same time it was pointed out that 

 most cells have an outer lining 

 or cell wall with soft contents 

 inside. To these contents was 

 given the name of the primordial 

 utric.e, which ultimately was shown 

 to be a gelatinous slimy substance 

 living inside the cell wall. In 1846 

 the name of protoplasm was given 

 to this substance of which cell 

 contents are composed. 



Protoplasm can exist without 

 any special protective envelope, 

 but it usually forms one for itself, 

 so that in a complete cell the proto- 

 plasm should be regarded as the 

 living substance in the cell, and the 

 envelope which it has itself formed 

 may be looked upon as the skin 

 of the cell. 



From a chemical point of view, 

 protoplasm is an exceedingly com- 

 plicated substance. As long as it is 

 living, there is a constant series of 

 chemical changes going on within 

 it. According to some, protoplasm 

 is composed of one very highly 

 complex substance, which itself is 

 built up of molecules which must 

 have an almost unimaginable com- 

 plexity. Others incline to the 

 view that there are in protoplasm 

 a number of simpler substances 

 more or less dependent upon each 

 other. Roughly speaking, the 

 composition of protoplasm may be 

 said to be somewhat allied to that 

 of albumen, and the term protein 

 is used to designate all substances 

 of an albuminous nature. 



Protoplasm in the interior of a 

 growing cell exhibits many curious 

 vital phenomena. As it nils up the 

 cell, the central part may be ob- 

 served to relax so as to form vacant 

 spaces or vacuoles. Between these 

 vacuoles the protoplasm may ar- 

 range itself into partitions, which 

 again split up into threads, stretch- 

 ing across the cell cavity. At other 

 times the growing protoplasm 

 becomes motile, and these move- 



6366 



ments can be observed with a good 

 microscope in such large cells as 

 have thin cell walls, particularly 

 when the protoplasm itself con- 

 tains a number of little dark 

 granules, as it often does. These 

 granules move backwards and for- 

 wards with the movements of the 

 protoplasm, enabling the latter to 

 be seen. Curiously enough, they 

 never pass into the cavities of the 

 vacuoles. 



A living protoplast, i.e. a mass 

 of protoplasm, is able to move its 

 parts, expand, contract, divide, 

 and fuse with another similar por- 

 tion. It can even utilise different 

 parts of itself for special functions. 

 It can produce definite chemical 

 compounds and excrete them when 

 necessary. It can secrete its own 

 cell wall, and it can also secrete 

 in the spaces of the vacuoles 

 within it a watery fluid, called cell 

 sap, in which there may occur 

 various substances such as sugar, 

 acids, and similar matters. 



Further, in the substance of the 

 protoplasm itself a gre t variety 

 of structures are produced in 

 different sorts of cells, which can 

 be definitely recognized under the 

 microscope, such as the cell nuc- 

 leus, granules of starch, and grains 

 of chlorophyll. These chlorophyll 

 elements are not essentially dif- 

 ferent from the protoplasm which 

 forms them, and in which they 

 remain during the whole of their 

 existence, but their green colour 

 renders them easily visible. Other 

 substances which may be formed 

 in the protoplasm include crystals 

 such as those of oxalate of lime, 

 and drops of fat, and all these 

 various products, as well as the 

 cell-wall itself, are the result of the 

 vital processes inherent in proto- 

 plasm, and have some reference to 

 the requirements and circumstances 

 of the moment. See Biology ; Cell ; 

 Life. 



Bibliography. Microscopic Foams 

 and Protoplasm, O. Biitschli, Eng. 

 trans. E. A. Minchin, 1894 ; The 

 Cell, E. B. Wilson, 2nd ed. 1900 ; 

 Protoplasm, its Definition, Chemis- 

 trv, and Structure, G. Mann, 1906 ; 

 The Cell, O. Hertwig, Eng. trans., 

 M. Campbell, 1909. 



Protopopoff, ALEXANDER (d. 

 1918). Russian statesman. For- 

 merly in the army, he became pro- 

 vincial delegate 

 of the Zemstvo 

 and marshal of 

 nobility in the 

 Volga district. 

 Elected to the 

 Duma, he was 

 at first a lead- 

 er of the liberal 

 party. As vice- 



Alex. Protopopoff, 



Russian statesman 



president of the 

 fourth duma, 



PROTOZOA 



he headed the parliamentary dele- 

 gation to Allied countries in tlu 

 spring of 1916, and on returning to 

 Russia was discovered to have en- 

 tered into secret negotiations with 

 the German minister at Stock- 

 holm for a separate peace. He be- 

 came minister of the interior in 

 Oct., 1916, and after the downfall 

 of Sturmer was virtually dictator, 

 and on the murder of the latter lit 

 became the most powerful of the 

 pro-German plotters. To further 

 his ends he entered upon a policy 

 of provoking the disturbances in 

 Petrograd which led directly to 

 the Revolution. He was tried by 

 the Bolshevists in July, 1918, and 

 shot in Moscow in September. 



Protopterusannectens. Species 

 of mud-fish. Found only in the 

 rivers of tropical Africa, it resembles 

 a bulky eel, and may attain a length 

 of 6 ft. The swimming bladder is 

 modified to serve the purpose of a 

 lung, so that the animal is able to 

 live for long periods out of water. 

 When the streams dry up in the 

 summer, the protopterus buries 

 itself in the mud, where it forms 

 a kind of cocoon, and remains dor- 

 mant until the wet season. It 

 seems to be nocturnal in habit, and 

 creeps over the mud in shallow 

 water by the aid of its limb-like 

 fins. In the breeding season the 

 male constructs a hole in the edge 

 of a swamp, and when the eggs 

 are deposited by the female, he 

 watches over them till they hatch. 

 By constantly waving his tail over 

 them he causes currents in the 

 water, and ensures their sufficient 

 aeration. In the early stages, the 

 young of the protopterus are very 

 much like the tadpole of a newt. 



Prototheria (Gr. protos, first ; 

 therion, wild beast). Lowest division 

 of the zoological class mammalia. 

 It includes only the ornithorhyn- 

 chus and the two spiny ant-eaters, 

 all of which are restricted to Aus- 

 tralasia and New Guinea. These 

 animals lay eggs and have only one 

 external excretory aperture. See 

 Animal ; Mammal. 



Protozoa (Gr. protos, first ; 

 zoon, living thing). Zoological 

 term for the phylum of the animal 

 kingdom, which includes the 

 lowest forms of all. They consist 

 of single cells, or of colonies of 

 single cells, each of which is 

 capable of separate existence and 

 of reproducing its kind. They are 

 distinguished from all other ani- 

 mals by the two features that in 

 the majority of cases the body 

 consists of a single cell of proto- 

 plasm which cannot be differen- 

 tiated into tissues, and that they 

 reproduce by the whole animal 

 breaking up into germ cells. In all 

 the higher animals the organism 



