September 3, 1915] 



SCIENCE 



299 



are produced does not in any way conflict 

 with the hypotheses already stated but is 

 really an accessory to them. Although 

 Gager probably had no such thought in 

 mind, his conception is in complete accord 

 with a theory of enzyme modifiability, which 

 at the same time presents a picture of the 

 manner in which the radiations affect pro- 

 toplasm. 



Early in the investigations the question 

 arose as to whether the effects observed in 

 the division of the egg might not be due to 

 a change caused by the radiation in the 

 permeability of the cell membranes to cer- 

 tain substances contained in the solution in 

 which the eggs developed. It is known that 

 surface changes due to the alteration of 

 permeability account for many of the phe- 

 nomena connected with the initiation of de- 

 velopment and cell division, and by analogy 

 it was argued that to similar changes might 

 be due the retardation of division rate as 

 well as other departures from normal as 

 they occur in the radiated eggs. To test 

 this question the writer undertook a series 

 of experiments^* in which several different 

 tests for permeability change were used 

 and all gave the_same result: that the X- 

 ray effects are not to be attributed to per- 

 meability changes caused by the radiation. 

 In the first method, the larvffi of Arenicola, 

 a marine worm, were employed, for it had 

 been found that, when these larvse are 

 brought into any solution that causes per- 

 meability changes, a yellow pigment is ex- 

 uded from the integument; no exudation 

 could be observed under the influence of 

 the radiation. The second method con- 

 sisted of experiments conducted with the 

 view to producing artificial parthenogene- 

 sis, for upon the basis of the current work- 

 ing hypothesis, artificial parthenogenesis is 



18 Ricliards, A., "Experiments on X-radiation 

 as the Cause of Permeability Changes," Amer. 

 Jour. Physiol., Vol. 36, 1915. 



due to the cytolysis of the cortical layer of 

 the protoplasm, which in its turn is corre- 

 lated with permeability changes on the egg 

 membrane; positive results from experi- 

 ments to cause this phenomenon would 

 therefore imply permeability changes. The 

 experiments were unsuccessful in the at- 

 tempt to cause parthenogenesis. Various 

 modifications of the indicator method were 

 used, all with the result that substances in 

 solution were found to enter the cell, which 

 had been stained with some neutral indica- 

 tor, in this case neutral red, after exactly 

 the same interval in both the radiated and 

 the unradiated control cells. This shows 

 that the radiation is ineffective in causing 

 permeability changes in the cell mem- 

 branes. These experiments warrant the 

 conclusion that permeability changes are 

 not the causal factors in the events which 

 follow radiation. 



Prom Gager's conclusions that radioac- 

 tivity is a stimulus to metabolic processes, 

 it may be inferred that the functions, as 

 cell division, which even remotely depend 

 on these processes would also be affected by 

 radiation. Such an inference is borne out 

 by the observations^'' made by the writer on 

 the rate of division in Planorbis eggs that 

 had been exposed to X-rays, for in these 

 experiments it was found that a light radi- 

 ation served to accelerate the first one or 

 two mitotic cycles that followed it; after 

 that injurious effects gradually asserted 

 themselves. A strong radiation was directly 

 inhibitive. The cytologieal study of the 

 eggs used in these experiments has not been 

 completed, so that it is as yet impossible to 

 correlate the observations on the living 

 eggs with changes in the finer details of 

 their structure. It is of course possible that 

 we have manifested in these physiological 



19 Richards, A., ' ' The Effect of X-rays on the 

 Kate of Cell Division in the Early Cleavage of 

 Planorbis," Biol. Bull, Vol. 27, 1914. 



