mitoses, and 3) a secondary effect, a reappear- 

 ance of mitoses which are different from normal 

 ones. 



The primary effect manifests itself in pyc- 

 nosis of the nucleus in the spireme stage, in an 

 abnormal distribution of chromosomes, and in 

 the formation of "hour-glass" figures, which 

 Alberti and Politzer call "pseudomitoses. " After 

 a 10-minute period of irradiation, the number 

 of "pseudomitoses" reaches 8%; after 40 minutes, 

 25%. The completion of "pseudomitoses" can 

 take place in two ways: by condensation of the 

 bridge and by appearance of asymmetrical 

 daughter nuclei. It is also possible to observe 

 the flowing of the whole chromatin material 

 from one cell to another; as a result one cell is 

 left without a nucleus and partial pycnosis 

 occurs, i. e. , the chromosomes migrate to 

 various poles and some [chromosomes] stick 

 together on the equator. The intermediate 

 period is characterized by pycnosis and vacuo- 

 lization of the nuclei. The abnormal divisions 

 with the secondary effect [of the X rays] are 

 different than with the primary ones. The sec- 

 ondary effect is most frequently characterized 

 by a lagging of the chromosomes. The authors 

 noted the greatest number of irregularities at 

 metaphase where the chromosomes were ob- 

 served to turn, disintegrate into fragments, and 

 wander off to the poles. As a result of the 

 irregular migrations of the chromosomes, 

 micronuclei form, the number of which increases 

 markedly on the fifth and eighth days after irra- 

 diation. Besides this, the authors observed 

 asynchrony of phases. One group of daughter 

 chromosomes could be in telophase while an- 

 other could be in prophase. The duration of the 

 primary effect does not depend on the dose, but 

 the length of the period without mitoses is largely 

 dependent on it. With 1/3 H the mitosis -less 

 stage lasts about 12 hours; with 1 H, a whole 

 day; with 4 H, 3 days; with 12 H, 5 days; with 

 20 H, 8 days. The secondary effect, moreover, 

 is very clearly dependent on the dose. Although 

 this question has not been solved by the authors, 

 30 days after exposure to 4 H only normal mi- 

 toses were observed. The primary effect 

 affects only those cells which were in a stage of 

 division or immediately prior to it at the time 

 of irradiation. The processes of division were 

 slowed down. The secondary effect affects those 

 cells which at the time of irradiation were in the 

 resting stage. 



Kanti [Canti?], Kemp, and Juel (1930*) demon- 

 strated that the number of mitoses diminishes 

 at the time of irradiation, dropping to zero and 

 then increasing once more. This slowing down 

 is particularly marked in the last phases of 

 division. 



Bersa (1927), several hours after irradiating 

 the roots of Zea mays , observed a strong 

 depression of nuclear division which increased 

 as the dosage was increased. 



The work of Pekarek (1927) occupies a 

 unique place in the annals of X radiology, both 

 by its thoroughness and by its versatility. For 

 his experiments he also used the seeds of Vicia 

 faba; he selected seeds of identical size for 

 irradiation. The seeds were planted in sawdust 

 and irradiated when they attained a length of 

 2 to 3 centimeters. On the thirteenth day after 

 the beginning of the experiment the rootlets of 

 the control plants began to lengthen and branch 

 out, whereas the rootlets of irradiated plants 

 showed no branching and were much shorter. 

 Pekarek explained the retardation of growth of 

 the irradiated plants as a halting of cell division. 

 Pekarek, like KOrnicke, notes an unevenness of 

 the rootlet surface after irradiation. The folds 

 spread through the epidermal, the subepidermal, 

 and the deeper layers. Pekarek thinks that the 

 folds are the result of unequal growth of the 

 phloem and the plerome because cells of the 

 phloem grow in length and plerome cells in 

 width. 



The observations made by Schwarz (1837*) 

 that nuclei tend to increase in size with age and 

 shrink when the cells become old were con- 

 firmed by Pekarek who measured nuclei along 

 two diameters. These measurements showed 

 Pekarek that the nuclear mass doubles with age. 

 The shape of the nucleus also changes; it be- 

 comes thinner and finally assumes the form of 

 a disk. The length of the nucleus increases with 

 age, the width remains about the same, and the 

 thickness diminishes with age. Under the influ- 

 ence of X rays, the nucleus assumes an ellip- 

 soidal shape (i. e. , it behaves like the nuclei 

 of normal cells which are located much farther 

 away from the tip of the root). This change in 

 the mass of the nucleus shows a tendency 

 towards transformation of the meristem tissue 

 into permanent [mature] ones under the influence 

 of X rays. In order to determine the frequency 

 of cell division, Pekarek made counts in control 

 and irradiated roots after 2, 5.5, 21, 28, 50, 

 72, 100, and 144 hours. The counts indicated 

 that shortly after irradiation the number of 

 divisions decreased almost to zero. The fre- 

 quency of nuclear divisions eventually increased, 

 but did not equal that of normal cells. The 

 diminution of frequency of divisions indicates 

 that irradiation affects not only the nuclei in the 

 process of division, but also those in the resting 

 stage. In addition, new divisions do not com- 

 mence for some time after irradiation. 



Pekarek also distinguishes between the pri- 

 mary and the secondary effects of X rays. He 

 considers primary effects to be abnormalities 

 in the division of cells that at the moment of 

 irradiation are in division. Secondary effects 

 (which he calls anomalous) take place in nuclei 

 that at the moment of irradiation are in the 

 resting stage. Immediately after irradiation 

 with small doses there are no observable 

 changes; 2 hours later, however, alongside 

 normal [mitotic] figures, pathological ones 



66 



