THE FUNDAMENTAL ORGANIZATION 57 



solved in strong acids, dilute alkalies, calcium carbonate and 

 sodium phosphate. 



There has been a tendency to regard chromatin as the most 

 important substance of the living cell, and the chromosome as the 

 most important nuclear structure. Important they doubtless are, 

 but in many cases chromatin is known as such only in the form of 

 chromosomes which belong to the derived and not to the funda- 

 mental organization (see p. 88). In other words, chromatin is 

 manufactured in the nucleus and the substances or substance from 

 which it is made are still more fundamental. There appears to be 

 little justification for Heidenhain's view of two kinds of chromatin, 

 one— oxy chromatin— unstainable with basic dyes, the other— basi- 

 chromatin — staining readily. A substance in the nucleus is either 

 chromatin or it is something else. 



With the growing use of the Feulgen nucleal reaction there is 

 reason to believe that a more precise definition of chromatin will 

 be developed. This reaction finds its explanation in Steudel's (1912) 

 analysis of thymonucleic acid of which the empirical formula is: 

 C43H65P4X15O34. 1 Under moderate hydrolysis with HC1 the purin 

 bodies are split off the molecule of thymonucleic acid and reducing 

 groups are freed. These behave like aldehydes and give the charac- 

 teristic red-violet color with Schiff's test (Magenta in the presence 

 of sulphuric acid). 



The nuclei of various groups of Protozoa give positive chromatin 

 reactions with this test, and it is a useful method in tracing the 

 development of chromatin in ex-conjugants or in the chromosomes 

 of the maturation divisions. (See Feulgen and Rossenbeck, 1924; 

 Bresslau and Scremin, 1924; Robertson, 1927; Zuelzer, 1927; 

 Jirovec, 1927; Reichenow, 1928, and infra pp. 93 and 315.) 



2. Other Substances of the Nucleus. — Belaf (1926) makes this state- 

 ment concerning nuclei of the Protozoa : " For the most part chro- 

 matin of the resting nucleus cannot be distinguished from the 

 ground substance of the nucleus (loc. cit., p. 241)." This refers to 

 the conditions of the living nucleus and not to fixed and stained 

 material. In the latter chromatin in the form of granules can be 



1 This may be written: 



(H 2 0)2— P— CsHioOs— C 5 H 4 N 6 (adenine) 



/ \ 



O O 



\ / 



P— C 6 H I0 O5— C6H4N5O (guanine) 



/ \ 



O O 



\ / 



P— CeHioOs— C5H5N2O2 (thymine) 



/ \ 

 O O 



\ / 

 (H20)2— P— C 6 Hio0 5 — C4H4N3O (cystocine) 



