342 CLASSICS OF MODERN SCIENCE 

 me that, at the present time, it is a necessary stage in the advancement 

 of our knowledge, and one which must be brought forward and 

 passed through, whether it prove right or wrong, in the future. In 

 this spirit I offer the following considerations, and it is in this spirit 

 that I should wish them to be received. 



THE GERM-PLASM 



I entirely agree with Strasburger when he says, "The specific quali- 

 ties of organisms are based upon nuclei" ; and I further agree with him 

 in many of his ideas as to the relation between the nucleus and cell- 

 body: "Molecular stimuli proceed from the nucleus into the sur- 

 rounding cytoplasm ; stimuli which, on the one hand, control the phe- 

 nomena of assimilation in the cell, and, on the other hand, give to the 

 growth of the cytoplasm, which depends upon nutrition, a certain 

 character peculiar to the species." "The nutritive cytoplasm assimi- 

 lates, while the nucleus controls the assimilation, and hence the sub- 

 stances assimilated possess a certain constitution and nourish in a 

 certain manner the cyto-idioplasm and the nuclear idioplasm. In this 

 way the cytoplasm takes part in the phenomena of construction, upon 

 which the specific form of the organism depends. This construc- 

 tive activity of the cyto-idioplasm depends upon the regulative 

 influence of the nuclei." The nuclei therefore "determine the spe- 

 cific direction in which an organism develops." 



The opinion — derived from the recent study of the phenomena of 

 fertilization — that the nucleus impresses its specific character upon the 

 cell, has received conclusive and important confirmation in the experi- 

 ments upon the regeneration of Infusoria, conducted simultaneously 

 by M. Nussbaum at Bonn, and by A. Gruber at Freiburg. Nuss- 

 baum's statement that an artificially separated portion of a Paramae- 

 cium, which does not contain any nuclear substance, immediately dies, 

 must not be accepted as of general application, for Gruber has kept 

 similar fragments of other Infusoria alive for several days. More- 

 over, Gruber had previously shown that individual Protozoa occur, 

 which live in a normal manner, and are yet without a nucleus, al- 

 though this structure is present in other individuals of the same 

 species. But the meaning of the nucleus is made clear by the fact, 

 published by Gruber, that such artificially separated fragments of 



