'2R{\ KADI \ TlON HlOl.OfiY 



(loiic, any attempt to treat death, division delay, etc., as having the same 

 cause in all cells is likely to he mislcadinji;. 



'This rc\ie\\ has l)e(Mi limited, for the most pari, to papers appearing 

 from the year H).'^') through the year 1950. A few earlier pieces of work 

 have been included when they seemed especially important for the topics 

 discussed, or when (hey were early papers in a series which continued 

 beyond 1935. A number of new lines of investigation have developed 

 since this manuscript was submitted. It has not been feasible to revise 

 the manuscript to include them. References to most of this work may 

 be found in fliese (1953). Wichterman (1953). and in Xudear Science 

 Abstracts. 



LETHAL EFFECTS 



Kind of Death. Many investigations have been concerned with the 

 lethal effects of radiation. However, the nature of the death is certainly 

 not the same in different cases. A variety of possible causes of death will 

 be discussed in the following paragraphs. 



First, there is death which occurs during or shortly after irradiation. 

 Numerous investigators have observed such death and described in more 

 or less detail the accompanying phenomena, such as loss of motility, 

 vacuolization and coagulation of the cytoplasm, and other changes. At 

 least a part of the investigations recorded in Tables 8-2 and 3 involve 

 phenomena preliminary to death. 



This type of death may occur very rapidly, as shown by the observa- 

 tions of Rentschler and Giese (1941) and Harvey (1942), with intense 

 flashes of ultraviolet. Some organisms, notably the ciliates, disintegrate 

 within a few seconds. In other cases, some minutes or even an hour or 

 so may elapse between irradiation and disintegration. 



The doses of ionizing radiation required to bring about this tj^pe of 

 death are very high. Dognon and Piffault (1931a) estimate the imme- 

 diate lethal dose for Paramecium to be about 500,000 r. Halberstaedter 

 (1938) showed that a dose of more than 100,000 r of X rays was needed 

 to immobilize Trypanosoma gambiense. Halberstaedter and Back (1942) 

 report loss of motility and cytolysis of the colonial flagellate Pandorina 

 morum after doses of 300,000-000,000 r. The very high doses required 

 for immediate killing have sometimes been considered characteristic of 

 the protozoa. However, Scott (1937) in his review points out that imme- 

 diate, as contrasted to delayed, death requires doses of similar magnitude 

 in other organisms. 



Giese and Leighton (1935a) report on the immobilization and vesicula- 

 tion of Paramecium, by monochromatic ultraviolet. In both cases 2804 A 

 appears to be more effective than other wave lengths. However, calcu- 

 lations of quantum efficiency, based on measurement of absorption of 

 paramecia. suggest that 2654, 2804, and 3025 A were about equally effec- 



