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SCIENCE 



[N. S. Vol. XLIV. No. 1129 



less remote points of time, but no biologist 

 limits himself to this relatively simple pur- 

 suit, since every living thing can be, at 

 least partly, identified also with the better 

 known portions of its ancestry. Indeed, 

 these so-called genetic similarities are so 

 striking and constant that one generation 

 can be inferred from another with con- 

 siderable precision. 



If there is a substantial basis for the 

 resemblances between parents and off- 

 spring, it must be the chromatin, for this 

 is the only material capable of being con- 

 tributed to each generation in essentially 

 equivalent values by all the members of a 

 given lineage. But if chromatin is respon- 

 sible for the partial identifications possible 

 between the individuals of two or more 

 generations, we must also suspect that the 

 specific recognition of a given individual 

 at any of the numerous phases of his life 

 is traceable to the same source. 



THE SYNTHESIS OP CHROMATIN 



Strictly speaking, ' ' chromatin " is a mor- 

 phological concept. Chemical analysis 

 shows that it contains a conjugated phos- 

 pho-protein provided with a nucleic acid 

 group, the latter a complex of phosphoric 

 acid and a nuclein base. During the so- 

 called resting state of the cell, this material 

 appears segregated in the nucleus. 



We must attach to this substance a de- 

 gree of specificity not less exact than the 

 specificities we are seeking to explain. In 

 this we have ample encouragement from 

 cytologists and geneticists. But the ques- 

 tion at once arises how chromatin can in- 

 crease in quantity during more than one 

 life cycle and yet lose none of its original 

 characteristics. Brothers, who in the one- 

 celled state derived from their mother the 

 kind or arrangement of chromatin which 

 in her father was associated with color- 

 blindness, not only exhibit this defect in 



their own persons, but between the ages of 

 25 and 55 produce each some 169,692,750,- 

 000 examples of the same factor, all trace- 

 able to their own original endowment. 



Compared with cytoplasm, the nucleus 

 seems meager in the diversity of its chem- 

 ical make-up. It is free from salts; it is 

 devoid of fats and carbohydrates. More- 

 over, iron and phosphorus, easily demon- 

 strable in the cytoplasm, are present in 

 nuclei in forms difficult to detect and for 

 that reason spoken of as masked or organic. 

 These facts are not altered by doubting the 

 localization of the iron in chromatin 2 or the 

 accuracy of the tests for organic phos- 

 phorus. 3 



From the constancy of their occurrence 

 we must conclude that both elements, as 

 nuclear constituents, are essential. How- 

 ever, their absence in inorganic form, 

 coupled with the general chemical poverty 

 of the nucleus, indicates that simple raw 

 materials for the synthesis of chromatin 

 are excluded by the nuclear membrane 

 (Macallum). 



This conclusion is out of harmony with 

 prevalent interpretation. Yet no one need 

 be misled. That nuclei are rendered con- 

 spicuous by staining, are scrupulously di- 

 vided in cleavage and maturation, and 

 combined with equal exactitude in fertili- 

 zation, are all beside the point. Further, 

 though no cell devoid of a certain propor- 

 tion of nuclear material can live, it is no 

 less true that a nucleus embarrassed by 

 the loss of cytoplasm also fails to maintain 

 itself. Chromatin, moreover, is present in 

 the bacteria, but not in the form of a nu- 

 cleus. Here its complete cytoplasmic syn- 

 thesis is not open to doubt. We are ready 

 enough to admit that the cytoplasm of nu- 



- References in Aristides Kanitz, ' ' Handbuch 

 d. Bioehemie, ' ' etc. Herausgegeben von Carl Op- 

 penheimer, pp. 253-254, Bd. II., Teil 1. 



3 B. B. Bensley, Biological Bulletin, Vol. X., pp. 

 49-65. 



