STRUCTURAL AND CHEMICAL ARCHITECTURE OF HOST CELLS 41 



same kinds and amounts of nucleotides present in the whole tissue. Mono- 

 nucleotides [adenosine monophosphate (AMP)] predominate in the non- 

 aqueous nuclei. However, a rapid isolation of nucleotides from aqueous 

 nuclei have revealed a markedly higher content of triphosphates, e.g., ATP. 

 The quantity of nucleotides amounts to about 1.7 % of the total mass. These 

 workers have also found that nuclei from metabohcally active tissues, such 

 as calf thymus or liver, have a higher content of nucleotides than is found in 

 nuclei of chicken erythrocytes or trout sperm, which are metabohcally 

 relatively inert. 



In wheat germ nuclei isolated by the Ca++-sucrose method, about 6 to 7 % 

 of the total nucleic acid plus protein is DNA (Johnston et al., 1957), and 

 about 1.5 % is E,NA, which is 2.5 times as concentrated in the whole tissue 

 as in the nuclei. 



Analyses of individual nuclei by spectrophotometric methods have re- 

 vealed the existence of classes of nuclei containing multiples of the DNA 

 content of the most frequent class. Such high values have been ascribed to 

 polyjaloidy. One approach to the analysis of effects of an increased chromo- 

 somal complement has been the study of the relation of DNA content to 

 nuclear volume. Such a correlation exists in the development of polytene 

 sahvary gland nuclei of Drosophila, whose giant chromosomes have been so 

 important in the development of cytogenetics. The gland nuclei may contain 

 up to 400 times the DNA of the anlage cells and are proportionately larger 

 (Swift, 1950a). However, in a wide variety of developing tissues, the DNA 

 content of the nuclei is quite mirelated to nuclear volume; the latter function 

 appears more closely related to protein content (Alfert, 1954). For example, 

 Alfert and Bern (1951) have reported that the mjection of estrogen into 

 ovariectomized rats doubles the volume of the nuclei of uterine gland cells 

 without change of their DNA content. In these instances, volume is presum- 

 ably determined by non-histone nuclear protein, since the DNA-histone ratio 

 tends to remain constant under conditions in which the variations of other 

 nuclear protem fractions may be considerable (Ris and Mirsky, 1949). 



Striking studies of the relation of the number of chromosome sets to cell 

 size and composition have been performed by Ogur, Lindegren, and their 

 collaborators. Increases of ploidy have proportionate effects on the size of 

 yeast cells. In Table III are presented data which demonstrate that a con- 

 stant relation exists between numbers of chromosome sets, the content per 

 cell of DNA, RNA, and metaphosphate in this organism, and the O2 con- 

 sumption and CO 2 production per ceU in air. 



b. On Nuclear Pailiology. Leuchtenberger (1950) has described cyto- 

 chemical changes occurring during pycnotic degeneration of nuclei of normal 

 and neoplastic tissues. During this process, the nuclei became spherical and 

 shrunken, nucleoh disappeared, and chromatin became homogeneous and 



