2 NUCLEUS 259 



proteins, whereas the other side upholds the micro-morphological 

 specificity of desoxyribose nucleic acid distribution. 



The fate of the desoxyribose nucleic acids in the cycle of nuclear 

 division favours the above hypothesis. When the nucleus undergoes 

 mitosis, desoxyribose nucleic acids are built up (increasing chromo- 

 philic tendency, nucleal reaction and ultraviolet absorption). In pro- 

 phase they appear to be embedded in the chromomeres, protecting 

 the specific groups during the cleavage of the chromosomes. When 

 their task is done, most of the desoxyribose nucleic acids migrate 

 from the chromomeres to the matrix of the chromosomes. As a result, 

 the latter absorbs stain to the full extent and the chromonemata thus 

 remain invisible during metaphase and anaphase; in this stage, there- 

 fore, nothing at all can be known of their exact morphology. In 

 telophase the desoxyribose nucleic acids are for the most part degraded 

 again. The chromosomes become transparent and it can be seen how 

 the chromonemata, losing their stainability, uncoil (Heitz, 1935, 

 p. 419) and disappear in the nuclear reticulum. 



There are parts of certain chromosomes which are called hetero- 

 chromatic, where the desoxyribose nucleic acids are not degraded after 

 cell division. When genes of euchromatic regions of the chromosome 

 come into the neighbourhood of heterochromatin by crossing over, 

 their manifestation is lost (Prokofyewa Belgorskaja, 1948; Lewis, 

 1950) or changed from dominant to recessive (McClintoc, 1950). 

 These facts indicate a screening effect of desoxyribose nucleic acids 

 on genes. 



In the view set forth here, the desoxyribose nucleic acids play a 

 passive part in heredity, in that, although they protect the genes, they 

 do not participate in their spontaneous propagation. By contrast, on 

 the analogy of the enzymes with nucleotides as prosthetic groups, an 

 active part may be assigned to them. Caspersson (1941), applying his 

 ultraviolet absorption method, discovered that vigorous protein 

 synthesis is initiated wherever nucleic acids appear; notably that 

 histones are formed as the result of the reaction of nucleic acids of 

 the ribose type (absorption maximum at 2900 A) and globuhns from 

 that of the nucleic acids of the desoxyribose type (absorption maxi- 

 mum at 2800 A). Caspersson, therefore, declares nucleic acids to be 

 necessary to any and every biological synthesis of proteins. In this 

 case the desoxyribose nucleic acid would be operative in the redupli- 



