21)0 UADIKIION HIOl-OCY 



The killing of nematode cj^gs hy ladiaiion may involve, in addition to 

 (l(>ath of (-('lis, rather diverse processes, such as abnormal development of 

 embryos and failure of the younp; worms to hatch. Several invest ij^at ions 

 with ultraviolet will be reviewed here. The eggs of Asrari.s have been, 

 in the past, favorite subjects for radiobiological research with X rays but 

 most of this work can be found summarized in Duggar (193G) and in the 

 tables of Dognon and Biancani (1948). 



Wright and McAlister (1934) examined eggs of Toxocara canis and 

 Toxascaris leonina for cmbryonation after exposure to 3()o0, 3130, 3022, 

 29()7, 2804, and 2050 A monochromatic ultraviolet. At the lowest dose 

 used (()840 ergs/mm-) effects were found only with the two shortest wave 

 lengths. Effects were found with 3022 A at a dose of 274,000 ergs/mm', 

 but even 1,370,000 ergs/mm^ of the two longest wave lengths had no 

 effect. 



These results are in agreement with those of Jones and HoUaender 

 (1944) with .4 scans lumhricoides. They found that energies of about 

 6,000,000 8,000,000 ergs/mmr of ultraviolet of the wave-length band 

 3500-4900 A were needed to prevent cmbryonation of a large part of the 

 eggs. Slightly higher energies were needed to prevent the hatching of the 

 eggs of the pinworm Enterobius vermicularis. These very long wave 

 lengths do have a lethal effect but only at very high doses. In an earlier 

 communication HoUaender ci al. (1940) show that the action spectrum for 

 the prevention of hatching of Enterobius eggs has a small peak at 2804 A 

 and then rises rapidly to the shortest wave length tested, 2280 A. This 

 action spectrum is similar to the absorption spectra of some proteins and 

 lipids. HoUaender and coworkers suggest, as possible modes of action, 

 hardening of an outside protein layer of the shell, change in composition of 

 the lipoid membrane, damage to the embryo, or production of toxic sub- 

 stances within the egg. The last is considered unlikely at the energies 

 used. 



In summarizing this section on kinds of death, it would appear that at 

 least the following categories of cell death can be recognized: (1) death 

 within a maximum of a few hours after irradiation, (2) death after con- 

 siderable periods of time but without division, (3) death at or shortly 

 after the first division, (4) death after several divisions, and (5) death fol- 

 lowing sexual processes. It seems quite possible that both (3) and (5) are 

 the result of gene mutations and chromosomal aberrations and so it is not 

 surprising to find that they occur in detectable amounts even at quite low 

 doses. The very high doses characteristic for (1), together with the 

 immediate changes involved, suggest extensive damage to cellular mate- 

 rials. The death in both (2) and (4) may involve disturbances in the 

 synthetic processes of the cell which finally lead to death when the 

 resources of the cell are exhausted. In some instances, mutational 

 changes can be excluded as a probable explanation of (2) and (4). When 



