58 INTRODUCTION TO CYTOLOGY 



develops condensed chromosomes, the nucleolar matter diminishes in 

 amount and commonly disappears completely. This long ago suggested 

 that it is with the chromosomal changes especially that the nucleolus is 

 concerned.-^ Kossel suggested that the albuminous nucleolar material 

 arises as one of the products formed when complex albumin-rich com- 

 pounds are spht to form albumin-poor "chromatin." 



Less evident are certain other functions which have been ascribed to 

 the nucleolus. It has often been regarded as a reserve material utilized 

 in some unknown manner by the protoplast.^^ To Strasburger (1895) its 

 behavior suggested a connection with the development of the achromatic 

 structures at the time of nuclear division (Chapter XI). Others have 

 made observations suggesting a role in secretion^" or yolk formation^^ in 

 animals. The evidence in a number of such cases has been adversely 

 criticized. ^- 



The Functions of the Nucleus. — Many years ago Claude Bernard 

 (1878) suggested that the nucleus is necessary for synthetic metabolism. 

 Since that time various investigators^^ have sought to test this hypothesis 

 by experiments on plant cells artifically deprived of their nuclei by means 

 of plasmolysis, centrifuging, direct section, cooling, or anesthesia. It 

 was observed that in these cells such activities as the formation of 

 cellulose membranes, assimilation, the utilization of reserves, growth, and 

 the division of plastids ceased at once or continued for only a short time. 

 The general conclusions were that these activities depend upon the pres- 

 ence of specific substances (building materials, enzymes, etc.) in the 

 cytoplasm, that such substances are elaborated with the cooperation of 

 the nucleus, and that the occurrence or non-occurrence of the activities 

 in question in enucleated masses of cytoplasm depends upon the presence 

 or absence of these substances at the time of the experiment. 



Analogous results have been obtained in certain experiments on 

 amoebae,^'* which can be cut into nucleate and enucleate pieces. The 



28 Flemming (1882), Strasburger (1884), F. M. Andrews (1901), Rhumbler (1893), 

 R. Hertwig (1898), Lubosch (1902), Farmer (1907), Sheppard (1909), Maziarski 

 (1910), Reed (1914), Schiirhoff (1918), Digby (1919), de Litardiere (19216), Ludford 

 (1922a), Cleland (1922, 1924), Lenoir (1923), Martens (1922), Van Camp (1924), 

 Latter (1926, 1932), Gates and Latter (1927), Zirkle (19286, 1931). 



29 M. Jorgensen (1913a), A. Meyer (1917, 1920), and many others. 



s« Macallum (1891), Maziarski (1911), Nakahara (1917, 1918a), Saguchi (1920), 

 Kinney (1926), Beams and Wu (1929). 



31 Macallum (1912), Lubosch (1902), Rohde (1903), Ludford (1921, 1922a), 

 Koch (1925), Gardiner (1927), Nath and Mehta (1929), Nath and Mohan (1929). 



32 M. Jorgensen (1913a), A. Meyer (1917, 1920), de Winiwarter (1925). 

 33KIebs (1887, 1888), Haberlandt (1887, 1919, 1921), Gerassimow (1890 et seq.), 



Townsend (1897), Palla (1889, 1890, 1906), Acqua (1891, 1910), van Wissehngh 

 (1909), BobiUoff-Preisser (1917), Heitz (1922). See Tischler (1921-1922; pp. 142- 

 147). 



3" Stole (1910), Lynch (1919), Phelps (1926), Becker (1926). 



