146 



NATURE 



[September 29, 1921 



discernment of a possible method of controlling 

 sex. 



It is interesting to note that pursuit of this specula- 

 tion leads one to a view of the paramount importance 

 of the individual as a whole in determining its charac- 

 ters, and in this respect recalls Darwin's hypothesis 

 of pangenesis. It may be pointed out, moreover, that 

 quite apart from theoretical questions the conditions 

 which determine whether an animal is to be herma- 

 phrodite or bisexual must be considered before any 

 reasonable hope can be entertained of understanding 

 the processes underlying sexual differentiation in a 

 bisexual species. Indeed, some inkling of the need 

 for sex might be obtained from an understanding of 

 the conditions resulting in hermaphroditism, and an 

 explanation of sex on purely physical lines would be 

 captivating from the point of view of the student of 

 nature as a whole. The old idea that an individual 

 is female because its metabolism is mainly anabolic, 

 or male because mainly katabolic, is unsatisfactory, 

 and it has already been pointed out that it is just as 

 likely that an individual is anabolic because of its 

 femaleness, or katabolic because of its maleness. 



In reviewing the incidence of hermaphroditism and 

 bisexuality throughout the animal kingdom (again ex- 

 cluding Protozoa) one cannot but be impressed by the 

 independence shown by the organism, which would 

 appear to be able to order its sexual manifestations in 

 a manner entirely independent of phylogenetic con- 

 siderations, and suggests such a ready response to con- 

 ditions of life as is perhaps not generally conceived. 



The practical points arising out oiF these speculations 

 may be summarised as follows : Is there a funda- 

 mental physical difference between sedentary and 

 active organisms in the whole body or in parts, and 

 if so, is this difference correlated in any way with par- 

 ticular sexual manifestations? To what degree is our 

 present knowledge of the sexual conditions in slow- 

 moving or fixed animals reliable? On the basis of the 

 speculations advanced here any animals which are 

 sedentary, fixed, or slow-moving may be suspected of 

 hermaphroditism in some form. 



No wholly satisfactory explanations have been ad- 

 vanced for either hermaphroditism, bisexuality, or 

 indeed sex itself. Sex Is universally expressed amongst 

 the higher living organisms at least, so that one is 

 tempted to ask : Is sex merely a property of living 

 matter and hermaphroditism that modification of the 

 property resultant upon the absence of motion In the 

 living organism, and bisexualltv that modification de- 

 pendent upon free motion ? For there appear to be 

 sufficient grounds for rejecting the Idea that animals 

 are sedentary because they are hermaphrodite. 



J. H. Orton. 



The Laboratory, Plymouth, September 19. 



The Separation of Mercury into Isotopes. 



Early in 1920 Harklns and Broeker reported a 

 separation of chlorine into isotopes, which amounted 

 at that time to an increase in density equal to 1550 

 parts per million. About six months later Bronsted 

 and von Hevesy reported a separation of mercury, 

 which was, however, only about one-thirtieth as 

 great, or 50 parts per million. On account of the 

 slightness of the density change reported for 

 mercury, the evidence that it had been separated did 

 not appear to be conclusive, so it seemed worth while 

 to attempt a confirmation by the same method — 

 that is, a vaporisation at low pressures. As a result 

 of 4 cuts of 2 on the heavy fraction or residue the 

 density has been Increased by 69 parts per million, 

 and by the same number of cuts on the light fraction 

 it has been decreased 62 parts, d" the total density 



NO. 2709, VOL. 108] 



change obtained is 133 parts pet million, or 0027 

 units of atomic weight. 



The mercury was purified by electrolysis, by five 

 fractional distillations at low pressure in a current 

 of pure air, and by one fractional distillation in a 

 high vacuum. 



The present evidence that an actual separation of 

 isotopes has been obtained with mercury rests largely 

 in the quantitative agreement between the results 

 of Br0nsted and von Hevesy and ourselves with 

 respect to the extent of the separation obtained by a 

 definite cut, which will be termed the efficiency of the 

 process. If the efficiency of our ideal apparatus, in 

 which solid carbon dioxide and ether were used for 

 cooling, is rated as 100 per cent., then the efficiency 

 attained by the previous investigators is 75 per cent., 

 while our less Ideal apparatus gave 93 per cent, when 

 operated slowly and as low as 80 per cent, when 

 operated rapidly. 



We have obtained evidence which seems to indicate 

 that a slight separation of the isotopes of mercury 

 has been secured by a very slow distillation at very 

 low pressures, though a more rapid distillation gave 

 no detectable difference in density. 



The relative changes produced in the atomic weights 

 of different elements by a definite cut may be termed 

 the separation coefficients. These have the values 

 listed below as determined by calculation, the 

 coefficients for chlorine compounds representing the 

 change in the atomic weight of chlorine. The cal- 

 culated coefficients are : — Neon, 000843 ; magnesium, 

 o-oo868 ; lithium, 000450; nickel, 000758; hydrogen 

 chloride, 0-00950 ; methyl chloride, 0-00690 ; chlorine, 

 0-00494; methylene chloride, 0-00413; chloroform, 

 0-00295 ; carbon tetrachloride, 0-00229 » ^"^ hydrogen 

 bromide, 0-00614. Thus the atomic weight changes 

 most rapidly when chlorine is used in the form of 

 hydrogen chloride. The experimentally determined 

 coefficient for mercury is 000570, which is not 

 specially large. 



The rate of separation of two isotopes is very nearly 

 proportional to the square of the difference of their 

 atomic weight (or molecular weight when a compound 

 Is used), to the product of the mol fractions of the 

 two isotopes, to the logarithm of the cut, and inversely 

 proportional to the atomic (or molecular) weight. This 

 statement and the above coefficients apply as well fo 

 molecular diffusion at low pressures as to vaporisa- 

 tion at low pressures. 



It is of interest to note that many molecular sub- 

 stances must appear in many isotopjc forms. Thus 

 if there are two isotopes of chlorine and three of 

 magnesium there are nine isotopic forms of MgCl, 

 and seven forms of CeCL, while If there are six 

 isotopes of mercury there are sixty-three isotopic forms 

 of Hg^CU, which occurs in the form of a vapour. 

 Five of the seven Isotopic hexachlorobenzenes also 

 occur In several Isomeric forms. Isotopes may be able 

 to produce stereoisomerism with respect to infra-red 

 rays. William D. Harkiks. 



R. S. MULLIKEN. 



University of Chicago, August -^i. 



Relation of the Hydrogen-ion Concentration of the Soil 

 to Plant Distribution. 



This subject has recently assumed prominence 

 among ecologlsts and soil chemists, and Dr. Atkins's 

 interesting letter, with its valuable data, published 

 in Nature for September 15 (p. 80), directs general 

 attention to it and to the need and scope for further 

 work thereon. 



It seems very desirable to bear In mind that there 

 are strong indications that the relation between the 



