,'il I UADIATION liUJLOUY 



iKiturc of the iiiliciilcd chaiifJics which are prochiccd tliaii with the mech- 

 anism !)>• which they are pnxhiced. 'I'he work of Powers (I'.)IS) with 

 raihoactix-e isotojx's in the mechuin is an exception, lie lonnd that tor 

 eijual activities, as measnred by an air ionization chamher and vibrating; 

 reed electrometer, P^' was four to six times as effective in producing death 

 after autogamy as a mixture of Sr«", Sr«", and ^''"'. It would Ix; expected 

 tliat the phosphorus would be eoneentrated in the nucleus but not the 

 strontium and yttrium. Rubin (1948) computed from Powers' data the 

 expected increase of specific ionization due to the concentration of phos- 

 phorus in the nucleus and came to the conclusion that it could not account 

 for the total difference in effect which Powers found. He concluded that 

 some other factor must be involved and was inclined to believe that it was 

 the transmutation phenomenon, i.e., the result of the radioactive disin- 

 tegration of phosphorus atoms incorporated in the molecules of the chro- 

 mosomes. A number of approximations of necessity enter the calcula- 

 tions so that it would seem well to withhold (inai judgement until further 

 investigations of this matter have been made. 



In summary, nuclear mutations have been induced in Paramecium 

 aurelia and are subject to ciuantitative study. In addition, several ill- 

 defined inheritable changes have been found after irradiation of various 

 protozoa. Further advances in understanding these changes must depend 

 on obtaining them in a situation in which definitive genetic analysis is 

 possible. 



MISCELLANEOUS EFFECTS 



Activation of Eggs. Loeb (1914) discovered that unfertilized eggs of 

 Arhacia and Chartopierus could be stimulated to l^egin parthenogenetic 

 development by exposure to ultraviolet from a ([uartz mercury vapor 

 lamp. Giese (1949) has recently reviewed the subject but a brief dis- 

 cussion of it seems desirable here. 



The activation of the sea urchin egg has been studied by several investi- 

 gators. This egg is mature when shed and activation is indicated by 

 membrane elevation and cleavage. The later cleavages in activated eggs 

 may be quite irregular, with spindle abnormalities and fragments of 

 chromatic material on the spindle (Nebel et al, 1937). Hollaender (1938) 

 has shown that wave lengths of 2()50 A and longer have very little effect on 

 the whole Arhacia egg. The curve of effectiveness rises sharply around 

 2400 A and is still rising at the shortest wave length used, 22()0 A (Fig. 

 8-0). This type of curve is a rather generalized one, resembling the 

 absorption curves for certain proteins and for lipids. Giese (1949) 

 believes that it may be the result of absorption in the lipids of the cell 

 membrane. It would appear that the curve for different eggs may not be 

 the same. Giese ( 1 938d) found no activation by 2537 A ultraviolet, in the 

 doses used, of the eggs of the sea urchin Sfrongyloccntrotus, but he (1939c) 



