PROTOZOA AND INVERTEBRATE EGGS 311 



Transfers were made every 10-12 days. The division rate was about one 

 per day. Although the exposed cultures continued to multiply through 

 many transfers, they eventually died out while control cultures survived. 

 Thus the cultures exposed to radium succumbed at the 190th transfer 

 while 16 control series were still aHve after more than 20(i transfers. It 

 would appear that the effects of sublethal exposure to radium and the 

 other agents were accumulati^•e o\'er the course of many generations of 

 cell division. However, no genetic analysis of the material was made, 

 and the method allows autogamy, and so gene recombination, to occur. 

 Various complex processes of selection of both the paramecia and their 

 accompanying bacteria are also possible. An interpretation in terms of 

 mechanism seems impossible without further analysis. 



Schaeffer (1946) reported an inherited change in size induced in the 

 giant multinuclear ameba Chaos chaos. Some of the amebae broke into 

 fragments following X irradiation. The largest fragments developed into 

 clones of normal size and the smallest died. However, some of the 

 medium-sized fragments grew into clones whose average volume was 

 about 60 per cent of the parent clone. One such clone was maintained 

 for four years. When this small clone was exposed to X rays, clones were 

 obtained which were still smaller. These latter clones had been main- 

 tained for three months at the time of the report. Schaeffer does not 

 propose a mechanism to explain these results. In the light of the multi- 

 nuclear condition of this species, it seems difficult to suppose that gene 

 mutations or chromosomal aberrations were involved. If fragmentation 

 into medium-sized pieces is really a necessary first step, interesting specu- 

 lations concerning the determination of size in such multinucleate proto- 

 plasmic masses might be made. However, no data on the frequency with 

 which the change has occurred are given, so that it is difficult to evaluate 

 the apparent correlation l)etween the size of the fragment and the occur- 

 rence of the variant. 



The self-reproducing cytoplasmic particle, kappa, of P. aurelia has been 

 shown to be inactivated by X rays (Freer, 1948, 1950), by nitrogen 

 mustard (Geckler, 1949), and by 2537 A ultraviolet (Kimball, 1950). 

 Freer (1950) finds that the curve of the logarithm of the number of par- 

 ticles against dose is not quite linear and suggests several sources of diffi- 

 culty which might explain the departure, since he believes that the inac- 

 tivation of kappa is basically a single-event phenomenon. Depending on 

 the interpretation, the true inactivation dose (37 per cent dose) is con- 

 sidered to lie between 3400 and 4000 r or at approximately 10,000 r. 

 Sensitive volumes calculated on this basis are in reasonable agreement 

 with the size of the particles which can be observed under the microscope. 

 Freer reports that microscopic examination showed that it takes some 2 

 to 3 days in the absence of cell division for the visible kappa particles to 

 disappear following X irradiation. 



