GENETIC AND CYTOLOGICAL EFFECTS 251 



to those induced by ultraviolet radiation. If they are not, it is possible 

 that the spectral limit of both classes of X-ray alterations is far below 

 the shortest ultraviolet wave length that can be used in biological experi- 

 ments, and that the mutations and chromosomal alterations characteristic 

 of the ultraviolet are of a type not occurring in appreciable frequency in 

 the X-ray progenies. 



EXPERIMENTAL PROCEDURES 



Genetic and cytological studies of the effects of ultraviolet radiation on 

 higher organisms are limited by the techni(iues which permit the investi- 

 gator to irradiate the germ cells effectively without killing the organism 

 or the cells being treated. Ultraviolet produces considerable physio- 

 logical damage, setting limits to the dosage; it is also low in penetrating 

 power, a disadvantage when deep-seated sex organs are being treated. 

 Both of these phenomena result from the high absorption of ultraviolet by 

 extranuclear constituents of the cells as well as by the nucleoproteins of 

 the chromosomes. A number of techniques are available, however, and it 

 is fortunate that they permit the irradiation of the germ cells of Droso- 

 pfiila and maize, thus making possible genetic and cytological comparison 

 with other mutagenic agents. Ultraviolet radiation and X rays have also 

 been used extensively with Neurospora, in which significant cytogenetic 

 comparisons could be made, but no comparative studies of the induced 

 alterations have been reported. 



Perfection of the technique of artificial insemination of Drosophila 

 females with treated spermatozoa would circumvent the difficulties of 

 reaching the sex cells of adult males with ultraviolet radiation, but 

 apparently all attempts to duplicate Gottschewski's (1937) artificial 

 insemination results have so far been unsuccessful. Two other methods, 

 however, have been developed: (1) irradiation of the pole cells of the 

 early embryo in the egg, and (2) irradiation of mature spermatozoa 

 through the ventral side of compressed abdomens of adult males. 



The polar cap technique was developed by Geigy (1931) after the early 

 work of Guyenot (1914) and Altenburg (1928) had demonstrated that 

 ultraviolet treatment of adult males gave only inconclusive results. The 

 pole cells are destined to enter the germ tract. At 75 min after fertiliza- 

 tion of the egg (at 24°C) the pole cells appear close to the surface at the 

 amicropolar end, w^here they remain for approximately 1 hr (Altenburg, 

 1934). In this position their nuclei can be readily reached by ultraviolet 

 radiation. The early experiments of Altenburg (1933, 1934) were made 

 with the angle of incidence of the ultraviolet at right angles to the vertical 

 axis of the egg, the lower portion cjf which could be shielded to reduce 

 injury to the developing embryo. More recently, it has been found that 

 a shift in the angle of incidence from a plane of 90° to one more nearly 



