LIVING SUBSTANCE 93 



the strands and nodal points of which the chromatic substance and 

 the nucleoli lie embedded in precisely the same manner as the solid 

 elements, the granules, etc., lie in the alveolar walls of the proto- 

 plasm. Indeed, as Biitschli has 

 shown, the similarity of the 

 relation even goes so far in in- 

 dividual cases that the achromatic 

 substance in the nucleus shows 

 precisely the same alveolar struc- 

 ture that the ground-mass of the 

 protoplasm as a rule possesses 

 (Fig. 33). 



All these structures are char- 

 acteristic Only Of the SO-Called FlG . 33 ._ Alveolar structure of the nucleus 

 resting-stage OI the Cell. As SOOn of a ganglion-cell. (After BUtschli.) 



as the latter prepares to multiply 



by division, very peculiar and very complex changes in the structure 

 of the nuclear substance appear ; these will be considered in detail 

 in another chapter. 



C. THE PHYSICAL PROPERTIES OF LIVING SUBSTANCE 



1. The Consistency of Living Substance 



Although the earlier investigators of the cell, such as Schleiden, 

 Mohl and others, as the result of direct observation, considered 

 the contents of the cell to be liquid, and compared its con- 

 sistency with that of slime, later the idea found wide accept- 

 ance that protoplasm is at bottom a solid substance. This 

 idea arose from purely theoretical considerations. Briicke ('61 ), 

 especially, thought that the cell-contents cannot be liquid, for the 

 reason that vital phenomena cannot possibly be associated with a 

 liquid substratum, but presuppose a definite organisation, and the 

 latter is not compatible with the nature of a liquid. Briicke's view 

 soon obtained many adherents, and appeared to be supported par- 

 ticularly by the theory of the reticular structure of protoplasm, as 

 maintained by Frommann and Heitzmann. It was believed that the 

 solid supporting-structure, with the organisation of which vital 

 phenomena are associated, was represented by the network. It 

 has turned ot, however, that the supposed reticular structure is 

 an optical delusion, and thus this basis for the view of the solid 

 consistency of protoplasm has been taken away. In reality, with 

 the present methods of microscopic investigation, only a strong 

 prejudice in favour of other and untenable theories can overlook 

 the fact that, with the exception of individual differentiations in 

 certain cells, protoplasm behaves physically like a liquid. 



The idea that vital phenomena can be associated with a solid 



