BIOLOGICAL EFFECTS OF RADIATIONS 



705 



Organisms vary widely in their susceptibility to roentgen radia- 

 tions. Protozoa and bacteria in vitro are unusually resistant. 



There is no doubt but that x-radiation produces changes in the 

 physiological activity of cells, but these changes are not as evident 

 as the morphological disturbances occurring in the nucleus and 

 cytoplasm. Such structural changes as lagging of chromosomes in 

 mitosis, failure of chromosomes to separate in meiosis, disintegra- 

 tion of chromatin, and coagulation of the protoplasm are produced. 

 Some physiological disturbances that have been noted are increased 

 permeability, increase in acidity, and changes in rate of respiration. 



Fig. 371. — Drawings of grasshopper embryos. The first figure in the upper left 

 is a normal embryo. The others are abnormal due to the x-radiation treatments. 

 Note that affected empryos have attempted to produce a secondary embryo. 



Mitotically active cells are usually more susceptible than resting 

 cells, and irradiated cells in the quiescent condition may appear 

 normal until the onset of mitosis and then disintegrate. Cells irra- 

 diated while in the process of dividing may complete the process 

 but be unable to negotiate a succeeding division. Destruction of 

 cells following irradiation may be delayed by holding them inactive 

 by low temperature or by some natural inhibitor. Some recovery 

 has been noted in a few instances in which quiescent cells were kept 

 inactive for a long period following irradiation. 



