400 
NATURE 
ments separately, and I am indebted to him for the 
result that the two classes of compounds can readily 
be separated by fractionation methods. 
This, I think, amounts to a proof that the electrons 
expelled as 8 rays come from a nucleus not capable of 
supplying electrons to or withdrawing them from the 
ring, though this ring is capable of gaining or losing 
electrons from the exterior during ordinary electro- 
chemical changes of valeacy. 
I regard van der Broek’s view, that the number 
representing the net positive charge of the nucleus is 
the number of the place which the element occupies 
in the periodic table when all the possible places from 
hydrogen to uranium are arranged in sequence, as 
practically proved so far as the relative value of the 
charge for the members of the end of the sequence, 
from thallium to uranium, is concerned. We are left 
uncertain as to the absolute value of the charge, 
because of the doubt regarding the exact number of 
rare-earth elements that exist. If we assume that all 
of these are known, the value for the positive charge 
of the nucleus of the uranium atom is about go. 
Whereas if we make the more doubtful assumption 
that the periodic table runs regularly, as regards 
numbers of places, through the rare-earth group, and 
that between barium and radium, for example, two 
complete long periods exist, the number is 96. In 
either case it is appreciably less than 120, the number 
were the charge equal to one-half the atomic weight, 
as it would be if the nucleus were made out of a par- 
ticles only. Six nuclear electrons are known to exist 
in the uranium atom, which expels in its changes six 
B rays. Were the nucleus made up of « particles 
there must be thirty or twenty-four respectively nuclear 
electrons, compared with ninety-six or 102 respectively 
in the ring. If, as has been suggested, hydrogen is a 
second component of atomic structure, there must be 
more than this. But there can be no doubt that there 
must be some, and that the central charge of the atom 
on Rutherford’s theory cannot be a pure positive 
charge, but must contain electrons, as van der Broek 
concludes. 
So far as I personally am concerned, this has re- 
sulted in a great clarification of my ideas, and it 
may be helpful to others, though no doubt there is 
little originality in it. The same algebraic sum of the 
positive and negative charges in the nucleus, when the 
arithmetical sum is different, gives what I call 
‘isotopes’? or ‘‘isotopic elements,’’ because they 
occupy the same place in the periodic table. They are 
chemically id-ntical, and save only as regards the 
relatively few physical properties which depend upon 
atomic mass directly, physically identical also. Unit 
changes of this nuclear charge, so reckoned algebraic- 
ally, give the successive places in the periodic table. 
For any one ‘‘place,” or any one nuclear charge, 
more than one number of electrons in the outer-ring 
system may exist, and in such a case the element 
exhibits variable valency. But such changes of num- 
ber, or of valency, concern only the ring and its 
external environment. There is no in- and out-going 
of electrons between ring and nucleus. 
FREDERICK SopDDy. 
Physical Chemistry Laboratory, 
University of Glasgow. 
Philosophy of Vitalism. 
In Nature of November 6 Prof. E. W. MacBride 
has made some critical remarks with regard to my 
proof of vitalism as discussed in the first of the four 
lectures which I had the honour to deliver before the 
University of .London in October. Will you kindly 
permit me to explain in how far I feel unable to 
accept Prof. MacBride’s criticism? 
NO. 2301, VOL. 92| 
I fully agree with him that vitalism has nothi 
do with the progress of zoology as a pure science 
the narrower sense of the word. As I have sai 
my ‘Biologie als selbstandige Grundwissenschi 
(second edition, 1911, p. 24): ‘‘The problem of the 
method of biology remains unaffected by the 
troversies between vitalism and mechanism.” 
But I cannot accept Prof. MacBride’s opinion abo 
the theoretical, or, if he would choose to say so, 
philosophical importance of the concept of entelechy. 
He believes ‘‘that at the best the conception of 
entelechy is of quite limited application.” He speaks 
of the fact that, under special experimental conditions 
a lizard may regenerate two tails instead of one, that — 
the egg of Ascidians (he might have added that of 
Ctenophores, a case well known to me from my own 
experiments) possesses a very limited faculty of regu-— 
lation, &c. But, has it not been for the very reason | 
of the fact that there are ‘‘limits of regulability” — 
that I have invented a rather complicated theory of © 
the possible relations between entelechy and matter — 
(see my Gifford lectures, vol. ii., p. 178ff., and the 
second of my London lectures)? Thus it appears, so 
I hope, that I have never neglected the limited char- 
acter of regulability and the dependence of the effects” 
of what I call entelechy on matter. Entelechy is not — 
omnipotent. But it seems to me that limitation does 
not mean non-existence. q 
For, on the other hand, there are very many cases — 
(development of isolated blastomeres or parts of the 
blastula of Echinoderms, &c., into small but complete — 
organisms, restitution of Clavellina, Tubularia,. &c.) 
where entelechy acts, so to say, in quite a pure 
manner. And it is on these cases, of course, that the 
concept of entelechy was founded in the first place. — 
Would not also a physicist whose aim it is to study — 
the laws of the reflection of light, prefer for his experi- — 
ments such materials, which do well reflect rays 
and do not show the phenomenon of absorption, or — 
only in a very small degree? Logically, in fact, one — 
single case of what I call harmonious equipotentiality 
would suffice to establish vitalism. But there are 
many cases. 
Prof. MacBride does not attack my analysis of har- © 
monious equipotentiality as such. And, in fact, the 
theory of organ-forming substances, which he advo- 
cates, cannot account at all for the differentiation of 
‘““harmonious-equipotential systems,” though we 
might accept it, perhaps, if there were only eggs, such 
as those of Ascidians, Ctenophores, &c. Organ-form-— 
ing substances have to be ordered or arranged during 
ontogeny; now this could only happen on the basis — 
of a machine, if we believe that it happens on a 
physico-chemical foundation altogether. But just a 
““machine’’ is excluded by the phenomenon of har- 
monious equipotentiality. j 
Thus I believe that, even if we concede to Prof. 
MacBride that the conception of entelechy is “of — 
quite limited application,’ we are entitled to say: In 
the theory of the harmonious-equipotential system the 
concept of entelechy must necessarily be applied. 
Hans Driescu. 
Heidelberg, November 12. 
THE courteous reply of Prof. Driesch to my letter © 
on vitalism which was published in Nature of Novem- 
ber 6 calls for only a few remarks from me. If — 
Prof. Driesch and I were discussing questions of — 
epistemology or of consciousness, questions in which — 
as an amateur I have taken an interest for many — 
years, it is possible that our points of view might not 
be so far apart; it would certainly be possible to — 
arrange a modus vivendi between them. But for me 
the value of a conception in zoology is its fruitfulness 
