Perthes assumes that all cells are sensitive to 

 X rays in some degree. Nevertheless, the 

 selective action of these rays is the essential 

 basis for the effect they have on tumors. Perthes 

 attaches special significance to the delayed 

 effect of irradiation, both for practical purposes 

 and for theoretical investigation. The time 

 after which the influence of irradiation begins to 

 manifest itself is extremely variable: the 

 higher the dose and the sensitivity of the irradi- 

 ated cell, the shorter the time interval. Perthes 

 explains the delayed effect by the fact that irra- 

 diation of the component parts of the cell, 

 chiefly the nucleus, induces chemical changes, 

 which proceed slowly and gradually increase 

 the amount of harmful substances (probably 

 insoluble products) that intensify first their 

 stimulating and later their harmful action. He 

 considers that his hypothesis is in complete 

 agreement with the available data. In the first 

 place, it shows that not only delay as such but 

 its duration is, to a certain extent, in inverse 

 ratio to the intensity of irradiation. In the sec- 

 ond place, this hypothesis offers a good expla- 

 nation for the fact that even during the period of 

 delay (i.e., before the appearance of the main 

 effects, the foremost of which are the abnormal 

 reactions of the cells) cellular reactions slow 

 down, etc. It also explains why in some object? 

 the stimulating effect becomes harmful and inju- 

 rious to the cells and tissues. Observations 

 indicate that the substance affecting the cell is 

 found at first in a minimum amount and then 

 steadily increases under the influence of irra- 

 diation. 



Alberti and Politzer (1924) in their first 

 article devoted to the action of X rays on organ- 

 isms write that even the very first biological 

 X-ray experiments showed that resting cells 

 were more resistant to the action of X rays than 

 cells in mitosis or in any of the stages of mito- 

 sis. If the various stages of mitosis are plotted 

 on the abscissa and the sensitivity to X rays 

 (expressing, for example, the number of dead 

 ova of the horse ascarid) is plotted on the ordi- 

 nate, we will then get a curve with a peak at 

 metaphase. Consequently, a small amount of 

 irradiation will disrupt only those mitoses 

 which are in metaphase, higher doses will 

 destroy those stages which are nearest to meta- 

 phase, both before and after. Finally, there 

 are doses which will lead to the necrosis of all 

 stages of mitosis. Greater doses than any of 

 the previous ones are required to kill the rest- 

 ing cells. 



Geller's observations (1924) on irradiated 

 beans, peas, wheat, and lilac buds permitted 

 him to conclude that the effect of radiation is 

 determined first by the species of the plant and 

 secondly by their condition. Unsprouted seeds 

 are more sensitive than germinated ones, 

 swollen [ soaked] seeds are more sensitive than 

 dry seeds. The age of the seeds does not affect 

 their sensitivity. Changes in external conditions 



(temperature, humidity of the air) show up 

 under irradiation. jQngling's* observation con- 

 cerning the significance of the point of applica- 

 tion of irradiation is very interesting. When the 

 tip is irradiated, growth in the tip slows down, 

 when the whole root is irradiated the side roots 

 cease their development. 



Seide's article (1925*) summarizes experi- 

 ments with animals, which indicate that major 

 injuries occur in early stages of development 

 with moderate doses of X rays and radium, 

 whereas older stages are completely unaffected 

 by these doses. Seide's own experiments reveal 

 an extreme sensitivity of the stages when chro- 

 mosomes begin to form (prophase). Stages 

 when the chromosomes are completely formed 

 (metaphase) are considerably less sensitive. 

 Rokhlina and GleTkhgevikht (1925*) compared the 

 action of X rays on sprouted seeds of Phaseolus 

 vulgaris and Vicia faba. By irradiating them 

 with identical dosages they established: 1) a 

 differential sensitivity of these two plants, and 

 2) a differential sensitivity among individuals. 

 What is most interesting is that the authors 

 discovered that the more sensitive the object, 

 the more quickly is stimulation followed by 

 retardation. Since retardation is induced by 

 very small doses in Vicia faba equina, this plant 

 is not suitable for investigation of the stimulat- 

 ing effect of X rays. Therefore, the authors 

 used Phaseolus vulgaris to study this effect. 

 When the seedlings of the two kinds of plants 

 were irradiated with an identical dose (1 1/2 

 HED), two weeks later the seedlings of P. 

 vulgaris were only slightly retarded in their 

 growth, whereas the seedlings of V. faba had 

 stopped growing altogether. 



Nemenov (1925 and 1926) considers that old 

 cells are most sensitive to X rays. The age of 

 the cell, in his view, is determined by the rela- 

 tion of the already lived part of its life to the 

 total life span of the given cell. The essence of 

 the biological process in the X -irradiated cell, 

 which leads to its aging, apparently consists of 

 disruption of metabolism and retention of the 

 products of metabolism within the cell. 



Iven (1925) also takes note of the differential 

 X -ray sensitivity shown chiefly by different 

 species of plants. After comparing the data of 

 numerous experiments, he came to the conclu- 

 sion that small seeds have low sensitivity to 

 X rays, and large seeds have high sensitivity. 

 The most sensitive objects are the seeds of 

 Vicia faba , which are the largest in size (of 

 those objects which have been subjected to irra- 

 diation). He also noted the importance of the 

 physiological condition of the seeds for success- 

 ful irradiation, pointing out that soaked seeds 

 react to irradiation to a considerably greater 

 degree than dry seeds do. Cytological exami - 

 nations have revealed that the nuclei of somatic 

 cells are more stable than those of germ cells. 

 The somatic cells, in turn, reveal a difference 



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