88 GENERAL PHYSIOLOGY 



various solid elements, or granules. In the foam-like protoplasm the- 

 granules always lie at the corners and angles where the foam- 

 vacuoles come together, never in the liquid of the bubbles 

 themselves. 



We have already spoken 1 of the idea of Altmann, who regards 

 the granules as the sole elementary parts of protoplasm, and the 

 intermediate substance between the granules as non-living. In 

 the light of Blitschli's investigations this view appears all the 

 more untenable. 



3. The Cell-Nucleus 



In recent years the cell-nucleus has become a favourite object 

 of morphological investigation. And here a psychological phe- 

 nomenon is to be noted, which has constantly repeated itself 

 in the history of the human mind, since mankind began to reflect 

 upon things this is the tendency toward exaggeration. The 

 earlier investigators of protoplasm, especially Max Schultze, had 

 convinced themselves that protoplasm shows important vital 

 phenomena, and at once by excessive generalisation the view was 

 promulgated that protoplasm is the sole bearer of vital phenomena, 

 while the nucleus possesses an accessory significance. Since then 

 it has been recognised that the nucleus participates prominently in 

 certain vital phenomena ; several investigators have shown that 

 it plays a very important role in reproduction, fertilization, secre- 

 tion, etc. Immediately the original view of the all-importance of 

 the protoplasm has by an extreme reaction become exchanged for 

 its opposite, that of the all-importance of the nucleus. As will be 

 seen in a later section, here, as so often, the truth lies between the 

 two. But every reaction is exaggerated. Opinions, like a pendu- 

 lum> go first to the two extremes, and only after some time does 

 the proper mean come to be maintained. Biology is indebted to 

 these investigations upon the nucleus for the fact that our 

 knowledge of it has been greatly extended. 2 



a. The Form of the Nucleus 



The form of the nucleus is very different in different cells. 



The first conception of the nucleus was formed from cells in 

 which within a circumscribed protoplasmic mass a single, more or 

 less spherical nucleus exists, which as regards its refractive power 

 and its consistency differs essentially from the surrounding proto- 

 plasm. It was found later that the nucleus stands in sharp con- 



1 Cf. p. 63, etfolg. 



* A. Zimmermann has recently made a comprehensive survey of the results of 

 research upon the nucleus, especially in plant-cells, in his book, Die Morphologic 

 und Physiologic des pflanzlichen Zellkernes : Eine kritische Litteraturstudie. Jena, 

 1896. 



