262 SOMI-: ASPECTS OF CELL-CHEMISTRY AND CELL-PHYSIOLOC Y 



secretion cease with its removal from the cytoplasm, while destructive 

 metabolism may long continue as manifested by the phenomena of 

 irritability and contractility. It is indicated by the position and move- 

 ments of the nucleus in relation to the food-supply and to the forma- 

 tion of specific cytoplasmic products. It harmonizes with the fact, 

 now universally admitted, that active exchanges of material go on 

 between nucleus and cytoplasm. The periodic changes of staining- 

 capacity undergone by the chromatin during the cycle of cell-life, 

 taken in connection with the researches of physiological chemists on 

 the chemical composition and staining-reactions of the nuclein-series, 

 indicate that the substance known as nucleic acid plays a leading part 

 in the constructive process. During the vegetative phase of the cell 

 this substance appears to enter into combination with proteid or 

 albuminous substance to form a nuclein. During its mitotic or repro- 

 ductive phase the albumin is split off, leaving the substance of the 

 chromosomes as nearly pure nucleic acid. When this is correlated 

 with the fact that the sperm-nucleus, which brings with it the pater- 

 nal heritage, likewise consists of nearly pure nucleic acid, the pos- 

 sibility is opened that this substance may be in a chemical sense not 

 only the formative centre of the nucleus but also a primary factor in 

 the constructive processes of the cytoplasm. 



The role of the nucleus in constructive metabolism is intimately 

 related with its role in morphological synthesis and thus in inheri- 

 tance ; for the recurrence of similar morphological characters must in 

 the last analysis be due to the recurrence of corresponding forms of 

 metabolic action of which they are the outward expression. That 

 the nucleus is in fact a primary factor in morphological as well as 

 chemical synthesis is demonstrated by experiments on unicellular 

 plants and animals, which prove that the power of regenerating lost 

 parts disappears with its removal, though the enucleated fragment 

 may continue to live and move for a considerable period. 



This fact establishes the presumption that the nucleus is, if not the 

 actual seat of the formative energy, at least the controlling factor in 

 that energy, and hence the controlling factor in inheritance. This 

 presumption becomes a practical certainty when we turn to the 

 facts of maturation, fertilization, and cell-division. All of these con- 

 verge to the conclusion that the chromatin is the most essential ele- 

 ment in development. In maturation the germ-nuclei are by an 

 elaborate process prepared for the subsequent union of equivalent 

 chromatic elements from the two sexes. By fertilization these ele- 

 ments are brought together and by mitotic division distributed with 

 exact equality to the embryonic cells. The result proves that the 

 spermatozoon is as potent in inheritance as the ovum, though the 

 latter contributes an amount of cytoplasm which is but an infini- 



