804 RADIATION BIOLOGY 



In the amphibian egg, X-ray doses of 50,000 r and more have been shown 

 by Duryee (1949) to produce enough solvation of the karyoplasm, or 

 presumptive spindle substance, to disorient certain of the chromosome 

 pairs within the nucleus. In the light of present information the 7-irradi- 

 ated Chaetopterus "chromosomes" that failed to move to the poles at 

 anaphase (Packard, 1918) were apparently acentric fragments instead of 

 chromosomes with radiation-induced destruction of the capacity to 

 develop spindle fibers, as postulated by Packard. Large doses applied 

 to dividing animal cells lead to an immediate fusion of all the metaphase 

 or anaphase chromosomes to form a single mass from which chromatin 

 material seems to flow toward opposite poles, but there appears to be no 

 change in spindle appearance or behavior (Alberti and Politzer, 1923, 

 1924; Carlson, 1941; Rugh, 1950). 



On the other hand, Marquardt (1938) and Roller (1943), whose 

 observations were made on Scilla root tips and Tradescantia microspores, 

 respectively, have concluded that small doses of X rays (360 r in Trad- 

 escantia) can lead to abnormal orientation or complete suppression of 

 spindle formation soon after treatment. Roller used delay of the chromo- 

 somes in attaining metaphase after breakdown of the nuclear membrane 

 and clumping of chromosomes without any orientation as evidence of the 

 absence of the metaphase spindle in the Tradescantia microspore. In 

 Scilla, absence of the spindle led to a certain disorientation of the meta- 

 phase and anaphase chromosomes, but the latter exhibited repulsion of 

 sister chromatids toward the opposite sides of the cell and a certain degree 

 of stickiness. 



CELL VIABILITY EFFECTS 



Nature of Effect. The presence of pyknotic and degenerating cells in 

 tissues after irradiation, the destruction of malignant growths, and the 

 failure of animals to hatch or seeds to germinate may all be the result of 

 irradiation-induced cell-lethal effects. We are concerned in this chapter 

 only with those cell-lethal effects that are evident very soon after 

 irradiation. 



Degenerative changes in irradiated cells of the tadpole brain and eye 

 are described as follows by Spear and Glucksmann (1938). At first there 

 is separation of chromatic from nonchromatic nuclear material, the 

 former gradually accumulating in the peripheral region of the nucleus, 

 while the latter forms a large central vacuole. Following this, the 

 nucleus breaks up into a number of parts, some of which contain deeply 

 staining chromatin scattered through the cytosome. Eventually the 

 cell undergoes fragmentation and dissolution. The chromatic elements 

 of the nucleus, which change from Feulgen positive to eosin positive, 

 gradually become smaller as they dissolve. A similar description is given 

 by Lasnitski (1943b, 1946) for the degeneration occurring in resting 



