THE MECHANISM OF LIFE 513 



the bottom by means of the delicate layer of slime, and continue 

 creeping. In non-nucleated pseudopodia of Difflugia at first a 

 secretion of slime takes place, but it soon ceases, and after a few 

 hours these protoplasmic masses likewise lose the power of attaching 

 themselves. 1 Finally, the loss of the power of producing cellulose 

 in the formation of a cell- wall, which Klebs ('87) observed in plant- 

 cells, is a very characteristic phenomenon. In his experiments Klebs 

 made use of the fact that harmless solutions of substances that 

 extract water cause the protoplasmic body of the plant-cell to 

 contract and to break up into separate protoplasmic globules, a 

 phenomenon that is termed by botanists " plasmolysis. " If he 

 put threads of Zygnema or Spirogyra into a 16 per cent, solution of 

 cane-sugar, the protoplasmic body of the cell in many cases broke 

 into two or more globules, of which one contained the single 

 nucleus. Both nucleated and non-nucleated pieces continued to 

 live, in many cases the latter even for six weeks. But during this 

 time a profound difference in the two was shown : the nucleated 

 pieces immediately surrounded themselves with a new cellulose 

 membrane, while the non-nucleated pieces always remained naked. 

 It follows from this experiment that the nucleus with its metabo- 

 lism takes an essential part in the formation of cellulose. But the 

 experiment is especially interesting from the fact that very recently 

 it has received a desirable completion by another experiment, 

 which Demoor (' 95) has performed upon the cells of Spyrogyra. 

 In a manner analogous to that in which by means of vivisection- 

 operations the influence of the nucleus upon the protoplasm was 

 excluded, Demoor succeeded by means of the suitable application 

 of various agents, such as chloroform, hydrogen, cold, etc., in 

 bringing to a standstill the life of the protoplasm while the nucleus 

 remained still active ; in other words, the activity of the 

 protoplasm was excluded. The result was that the nucleus 

 remained living for a considerable time undisturbed, just as 

 after the exclusion of the nucleus the protoplasm shows 

 normal vital phenomena for a considerable time. In Demoor's 

 experiments the vital activity of the nucleus expressed itself just 

 as in the normal life of the cell, pre-eminently by the phenomena 

 of nuclear division. The nucleus proceeded to divide as normally, 

 and to form the well-known complex mitotic figures, and soon two 

 nuclei appeared and separated from one another. 2 While, however, 

 in the undisturbed cell upon the separation of the two nuclei in 

 the protoplasm a new cellulose membrane is always formed 

 immediately, completing the division of the whole cell into two 

 daughter-cells, in Demoor's experiments the formation of such a 

 membrane was invariably absent, although the nucleus still con- 



1 Cf. Verworn ('90, 1 ). 



2 [Cf. hereupon Loeb and Hardesty ('95), Loeb ('95 ; '96, 1), Morgan ('96), and 

 Norman ('96).] 



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