NUCLEUS AFTER 1860. 101 



given up, and the existence of living masses, without any 

 nucleus, is admitted by Hackel, as it was by Naegeli, A. Braun, 

 Cohn, Briicke, and many others, before and since. He holds 

 the plasma to be the " active material substratum of life, and 

 which thus in a certain sense may be designated the * life-stuff,' 

 or, in a stricter sense, the ' living matter'" (p. 275). As to the 

 nucleus, he expresses himself very doubtfully, and wishes to 

 associate it with the formative power of the protoplasm ; then he 

 -says, in commenting on Beale's theory " Certainly the nucleus, 

 as regards its origin, is to be looked upon as a differentiation- 

 product of the protoplasm, but in the sense that now the 

 plasma and nucleus stand beside each other as co-ordinated 

 parts, as to a certain extent different organs of equal rank, and 

 which perform different functions" (p. 287). Then he follows 

 much the same theory as Virchow, and assigns to the nucleus 

 the power of propagation and of inheritance of hereditary 

 character, while to the plasma belong the nutrition and adapta- 

 tion to outward circumstances. While " in the cytods, in which 

 the nucleus and plasma are not yet differentiated, we have to 

 regard the whole plasma as the common organ of both func- 

 tions" (p. 288). This, of course, gives up the idea of three, or 

 even two distinct parts, as essential to the vital unit, which is 

 the characteristic of the cell theory. The question is thus re- 

 duced to the use of the nucleus as an organ in certain physio- 

 logical individuals of low order. (See p. 58.) 



On this much-vexed question of the nucleus we 

 have seen that Ley dig, in 1857, while he rejected the 

 cell wall, still held that the most important part of the 

 cell was the nucleus, which, as it were, animated the 

 protoplasm surrounding it. Briicke, on the other 

 hand, before Hackel, states that "the constancy of the 

 appearance of the nucleus is subject to essential limi- 

 tations if, as cannot be avoided, the cells of cryptogams 

 are also considered, and it is not assumed that the 

 nucleus must be present even where it is invisible" 



